<div class="head">
    <p><a href="http://www.w3.org/"><img height=48 alt=W3C src="http://www.w3.org/Icons/w3c_home" width=72></a>

    <h1 id="title">Selectors</h1>

    <h2>W3C Working Draft 15 December 2005</h2>

    <dl>

        <dt>This version:

        <dd><a href="http://www.w3.org/TR/2005/WD-css3-selectors-20051215">
            http://www.w3.org/TR/2005/WD-css3-selectors-20051215</a>

        <dt>Latest version:

        <dd><a href="http://www.w3.org/TR/css3-selectors">
            http://www.w3.org/TR/css3-selectors</a>

        <dt>Previous version:

        <dd><a href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113">
            http://www.w3.org/TR/2001/CR-css3-selectors-20011113</a>

        <dt><a name=editors-list></a>Editors:

        <dd class="vcard"><span class="fn">Daniel Glazman</span> (Invited Expert)</dd>

        <dd class="vcard"><a lang="tr" class="url fn" href="http://www.tantek.com/">Tantek &Ccedil;elik</a> (Invited Expert)

        <dd class="vcard"><a href="mailto:ian@hixie.ch" class="url fn">Ian Hickson</a> (<span
            class="company"><a href="http://www.google.com/">Google</a></span>)

        <dd class="vcard"><span class="fn">Peter Linss</span> (former editor, <span class="company"><a
            href="http://www.netscape.com/">Netscape/AOL</a></span>)

        <dd class="vcard"><span class="fn">John Williams</span> (former editor, <span class="company"><a
            href="http://www.quark.com/">Quark, Inc.</a></span>)

    </dl>

    <p class="copyright"><a
        href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">
        Copyright</a> &copy; 2005 <a href="http://www.w3.org/"><abbr
        title="World Wide Web Consortium">W3C</abbr></a><sup>&reg;</sup>
        (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts
   Institute of Technology">MIT</abbr></a>, <a
            href="http://www.ercim.org/"><acronym title="European Research
   Consortium for Informatics and Mathematics">ERCIM</acronym></a>, <a
            href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved.  W3C
        <a
            href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
        <a
            href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>,
        <a
            href="http://www.w3.org/Consortium/Legal/copyright-documents">document
            use</a> rules apply.

    <hr title="Separator for header">

</div>

<h2><a name=abstract></a>Abstract</h2>

<p><em>Selectors</em> are patterns that match against elements in a
    tree. Selectors have been optimized for use with HTML and XML, and
    are designed to be usable in performance-critical code.</p>

<p><acronym title="Cascading Style Sheets">CSS</acronym> (Cascading
    Style Sheets) is a language for describing the rendering of <acronym
        title="Hypertext Markup Language">HTML</acronym> and <acronym
        title="Extensible Markup Language">XML</acronym> documents on
    screen, on paper, in speech, etc. CSS uses Selectors for binding
    style properties to elements in the document. This document
    describes extensions to the selectors defined in CSS level 2. These
    extended selectors will be used by CSS level 3.

<p>Selectors define the following function:</p>

<pre>expression &#x2217; element &rarr; boolean</pre>

<p>That is, given an element and a selector, this specification
    defines whether that element matches the selector.</p>

<p>These expressions can also be used, for instance, to select a set
    of elements, or a single element from a set of elements, by
    evaluating the expression across all the elements in a
    subtree. <acronym title="Simple Tree Transformation
  Sheets">STTS</acronym> (Simple Tree Transformation Sheets), a
    language for transforming XML trees, uses this mechanism. <a href="#refsSTTS">[STTS]</a></p>

<h2><a name=status></a>Status of this document</h2>

<p><em>This section describes the status of this document at the
    time of its publication. Other documents may supersede this
    document. A list of current W3C publications and the latest revision
    of this technical report can be found in the <a
        href="http://www.w3.org/TR/">W3C technical reports index at
        http://www.w3.org/TR/.</a></em></p>

<p>This document describes the selectors that already exist in <a
    href="#refsCSS1"><abbr title="CSS level 1">CSS1</abbr></a> and <a
    href="#refsCSS21"><abbr title="CSS level 2">CSS2</abbr></a>, and
    also proposes new selectors for <abbr title="CSS level
  3">CSS3</abbr> and other languages that may need them.</p>

<p>The CSS Working Group doesn't expect that all implementations of
    CSS3 will have to implement all selectors. Instead, there will
    probably be a small number of variants of CSS3, called profiles. For
    example, it may be that only a profile for interactive user agents
    will include all of the selectors.</p>

<p>This specification is a last call working draft for the the <a
    href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>
    (<a href="/Style/">Style Activity</a>). This
    document is a revision of the <a
        href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113/">Candidate
        Recommendation dated 2001 November 13</a>, and has incorporated
    implementation feedback received in the past few years. It is
    expected that this last call will proceed straight to Proposed
    Recommendation stage since it is believed that interoperability will
    be demonstrable.</p>

<p>All persons are encouraged to review and implement this
    specification and return comments to the (<a
        href="http://lists.w3.org/Archives/Public/www-style/">archived</a>)
    public mailing list <a
        href="http://www.w3.org/Mail/Lists.html#www-style">www-style</a>
    (see <a href="http://www.w3.org/Mail/Request">instructions</a>). W3C
    Members can also send comments directly to the CSS Working
    Group.
    The deadline for comments is 14 January 2006.</p>

<p>This is still a draft document and may be updated, replaced, or
    obsoleted by other documents at any time. It is inappropriate to
    cite a W3C Working Draft as other than &quot;work in progress&quot;.

<p>This document may be available in <a
    href="http://www.w3.org/Style/css3-selectors-updates/translations">translation</a>.
    The English version of this specification is the only normative
    version.

<div class="subtoc">

    <h2><a name=contents>Table of contents</a></h2>

    <ul class="toc">
        <li class="tocline2"><a href="#context">1. Introduction</a>
            <ul>
                <li><a href="#dependencies">1.1. Dependencies</a> </li>
                <li><a href="#terminology">1.2. Terminology</a> </li>
                <li><a href="#changesFromCSS2">1.3. Changes from CSS2</a> </li>
            </ul>
        <li class="tocline2"><a href="#selectors">2. Selectors</a>
        <li class="tocline2"><a href="#casesens">3. Case sensitivity</a>
        <li class="tocline2"><a href="#selector-syntax">4. Selector syntax</a>
        <li class="tocline2"><a href="#grouping">5. Groups of selectors</a>
        <li class="tocline2"><a href="#simple-selectors">6. Simple selectors</a>
            <ul class="toc">
                <li class="tocline3"><a href="#type-selectors">6.1. Type selectors</a>
                    <ul class="toc">
                        <li class="tocline4"><a href="#typenmsp">6.1.1. Type selectors and namespaces</a></li>
                    </ul>
                <li class="tocline3"><a href="#universal-selector">6.2. Universal selector</a>
                    <ul>
                        <li><a href="#univnmsp">6.2.1. Universal selector and namespaces</a></li>
                    </ul>
                <li class="tocline3"><a href="#attribute-selectors">6.3. Attribute selectors</a>
                    <ul class="toc">
                        <li class="tocline4"><a href="#attribute-representation">6.3.1. Representation of attributes and attributes values</a>
                        <li><a href="#attribute-substrings">6.3.2. Substring matching attribute selectors</a>
                        <li class="tocline4"><a href="#attrnmsp">6.3.3. Attribute selectors and namespaces</a>
                        <li class="tocline4"><a href="#def-values">6.3.4. Default attribute values in DTDs</a></li>
                    </ul>
                <li class="tocline3"><a href="#class-html">6.4. Class selectors</a>
                <li class="tocline3"><a href="#id-selectors">6.5. ID selectors</a>
                <li class="tocline3"><a href="#pseudo-classes">6.6. Pseudo-classes</a>
                    <ul class="toc">
                        <li class="tocline4"><a href="#dynamic-pseudos">6.6.1. Dynamic pseudo-classes</a>
                        <li class="tocline4"><a href="#target-pseudo">6.6.2. The :target pseudo-class</a>
                        <li class="tocline4"><a href="#lang-pseudo">6.6.3. The :lang() pseudo-class</a>
                        <li class="tocline4"><a href="#UIstates">6.6.4. UI element states pseudo-classes</a>
                        <li class="tocline4"><a href="#structural-pseudos">6.6.5. Structural pseudo-classes</a>
                            <ul>
                                <li><a href="#root-pseudo">:root pseudo-class</a>
                                <li><a href="#nth-child-pseudo">:nth-child() pseudo-class</a>
                                <li><a href="#nth-last-child-pseudo">:nth-last-child()</a>
                                <li><a href="#nth-of-type-pseudo">:nth-of-type() pseudo-class</a>
                                <li><a href="#nth-last-of-type-pseudo">:nth-last-of-type()</a>
                                <li><a href="#first-child-pseudo">:first-child pseudo-class</a>
                                <li><a href="#last-child-pseudo">:last-child pseudo-class</a>
                                <li><a href="#first-of-type-pseudo">:first-of-type pseudo-class</a>
                                <li><a href="#last-of-type-pseudo">:last-of-type pseudo-class</a>
                                <li><a href="#only-child-pseudo">:only-child pseudo-class</a>
                                <li><a href="#only-of-type-pseudo">:only-of-type pseudo-class</a>
                                <li><a href="#empty-pseudo">:empty pseudo-class</a></li>
                            </ul>
                        <li class="tocline4"><a href="#negation">6.6.7. The negation pseudo-class</a></li>
                    </ul>
                </li>
            </ul>
        <li><a href="#pseudo-elements">7. Pseudo-elements</a>
            <ul>
                <li><a href="#first-line">7.1. The ::first-line pseudo-element</a>
                <li><a href="#first-letter">7.2. The ::first-letter pseudo-element</a>
                <li><a href="#UIfragments">7.3. The ::selection pseudo-element</a>
                <li><a href="#gen-content">7.4. The ::before and ::after pseudo-elements</a></li>
            </ul>
        <li class="tocline2"><a href="#combinators">8. Combinators</a>
            <ul class="toc">
                <li class="tocline3"><a href="#descendant-combinators">8.1. Descendant combinators</a>
                <li class="tocline3"><a href="#child-combinators">8.2. Child combinators</a>
                <li class="tocline3"><a href="#sibling-combinators">8.3. Sibling combinators</a>
                    <ul class="toc">
                        <li class="tocline4"><a href="#adjacent-sibling-combinators">8.3.1. Adjacent sibling combinator</a>
                        <li class="tocline4"><a href="#general-sibling-combinators">8.3.2. General sibling combinator</a></li>
                    </ul>
                </li>
            </ul>
        <li class="tocline2"><a href="#specificity">9. Calculating a selector's specificity</a>
        <li class="tocline2"><a href="#w3cselgrammar">10. The grammar of Selectors</a>
            <ul class="toc">
                <li class="tocline3"><a href="#grammar">10.1. Grammar</a>
                <li class="tocline3"><a href="#lex">10.2. Lexical scanner</a></li>
            </ul>
        <li class="tocline2"><a href="#downlevel">11. Namespaces and down-level clients</a>
        <li class="tocline2"><a href="#profiling">12. Profiles</a>
        <li><a href="#Conformance">13. Conformance and requirements</a>
        <li><a href="#Tests">14. Tests</a>
        <li><a href="#ACKS">15. Acknowledgements</a>
        <li class="tocline2"><a href="#references">16. References</a>
    </ul>

</div>

<h2><a name=context>1. Introduction</a></h2>

<h3><a name=dependencies></a>1.1. Dependencies</h3>

<p>Some features of this specification are specific to CSS, or have
    particular limitations or rules specific to CSS. In this
    specification, these have been described in terms of CSS2.1. <a
        href="#refsCSS21">[CSS21]</a></p>

<h3><a name=terminology></a>1.2. Terminology</h3>

<p>All of the text of this specification is normative except
    examples, notes, and sections explicitly marked as
    non-normative.</p>

<h3><a name=changesFromCSS2></a>1.3. Changes from CSS2</h3>

<p><em>This section is non-normative.</em></p>

<p>The main differences between the selectors in CSS2 and those in
    Selectors are:

<ul>

    <li>the list of basic definitions (selector, group of selectors,
        simple selector, etc.) has been changed; in particular, what was
        referred to in CSS2 as a simple selector is now called a sequence
        of simple selectors, and the term "simple selector" is now used for
        the components of this sequence</li>

    <li>an optional namespace component is now allowed in type element
        selectors, the universal selector and attribute selectors</li>

    <li>a <a href="#general-sibling-combinators">new combinator</a> has been introduced</li>

    <li>new simple selectors including substring matching attribute
        selectors, and new pseudo-classes</li>

    <li>new pseudo-elements, and introduction of the "::" convention
        for pseudo-elements</li>

    <li>the grammar has been rewritten</li>

    <li>profiles to be added to specifications integrating Selectors
        and defining the set of selectors which is actually supported by
        each specification</li>

    <li>Selectors are now a CSS3 Module and an independent
        specification; other specifications can now refer to this document
        independently of CSS</li>

    <li>the specification now has its own test suite</li>

</ul>

<h2><a name=selectors></a>2. Selectors</h2>

<p><em>This section is non-normative, as it merely summarizes the
    following sections.</em></p>

<p>A Selector represents a structure. This structure can be used as a
    condition (e.g. in a CSS rule) that determines which elements a
    selector matches in the document tree, or as a flat description of the
    HTML or XML fragment corresponding to that structure.</p>

<p>Selectors may range from simple element names to rich contextual
    representations.</p>

<p>The following table summarizes the Selector syntax:</p>

<table class="selectorsReview">
    <thead>
    <tr>
        <th class="pattern">Pattern</th>
        <th class="meaning">Meaning</th>
        <th class="described">Described in section</th>
        <th class="origin">First defined in CSS level</th></tr>
    <tbody>
    <tr>
        <td class="pattern">*</td>
        <td class="meaning">any element</td>
        <td class="described"><a
            href="#universal-selector">Universal
            selector</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E</td>
        <td class="meaning">an element of type E</td>
        <td class="described"><a
            href="#type-selectors">Type selector</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E[foo]</td>
        <td class="meaning">an E element with a "foo" attribute</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E[foo="bar"]</td>
        <td class="meaning">an E element whose "foo" attribute value is exactly
            equal to "bar"</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E[foo~="bar"]</td>
        <td class="meaning">an E element whose "foo" attribute value is a list of
            space-separated values, one of which is exactly equal to "bar"</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E[foo^="bar"]</td>
        <td class="meaning">an E element whose "foo" attribute value begins exactly
            with the string "bar"</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E[foo$="bar"]</td>
        <td class="meaning">an E element whose "foo" attribute value ends exactly
            with the string "bar"</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E[foo*="bar"]</td>
        <td class="meaning">an E element whose "foo" attribute value contains the
            substring "bar"</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E[hreflang|="en"]</td>
        <td class="meaning">an E element whose "hreflang" attribute has a hyphen-separated
            list of values beginning (from the left) with "en"</td>
        <td class="described"><a
            href="#attribute-selectors">Attribute
            selectors</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E:root</td>
        <td class="meaning">an E element, root of the document</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:nth-child(n)</td>
        <td class="meaning">an E element, the n-th child of its parent</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:nth-last-child(n)</td>
        <td class="meaning">an E element, the n-th child of its parent, counting
            from the last one</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:nth-of-type(n)</td>
        <td class="meaning">an E element, the n-th sibling of its type</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:nth-last-of-type(n)</td>
        <td class="meaning">an E element, the n-th sibling of its type, counting
            from the last one</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:first-child</td>
        <td class="meaning">an E element, first child of its parent</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E:last-child</td>
        <td class="meaning">an E element, last child of its parent</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:first-of-type</td>
        <td class="meaning">an E element, first sibling of its type</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:last-of-type</td>
        <td class="meaning">an E element, last sibling of its type</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:only-child</td>
        <td class="meaning">an E element, only child of its parent</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:only-of-type</td>
        <td class="meaning">an E element, only sibling of its type</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:empty</td>
        <td class="meaning">an E element that has no children (including text
            nodes)</td>
        <td class="described"><a
            href="#structural-pseudos">Structural
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:link<br>E:visited</td>
        <td class="meaning">an E element being the source anchor of a hyperlink of
            which the target is not yet visited (:link) or already visited
            (:visited)</td>
        <td class="described"><a
            href="#link">The link
            pseudo-classes</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E:active<br>E:hover<br>E:focus</td>
        <td class="meaning">an E element during certain user actions</td>
        <td class="described"><a
            href="#useraction-pseudos">The user
            action pseudo-classes</a></td>
        <td class="origin">1 and 2</td></tr>
    <tr>
        <td class="pattern">E:target</td>
        <td class="meaning">an E element being the target of the referring URI</td>
        <td class="described"><a
            href="#target-pseudo">The target
            pseudo-class</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:lang(fr)</td>
        <td class="meaning">an element of type E in language "fr" (the document
            language specifies how language is determined)</td>
        <td class="described"><a
            href="#lang-pseudo">The :lang()
            pseudo-class</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E:enabled<br>E:disabled</td>
        <td class="meaning">a user interface element E which is enabled or
            disabled</td>
        <td class="described"><a
            href="#UIstates">The UI element states
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E:checked<!--<br>E:indeterminate--></td>
        <td class="meaning">a user interface element E which is checked<!-- or in an
      indeterminate state--> (for instance a radio-button or checkbox)</td>
        <td class="described"><a
            href="#UIstates">The UI element states
            pseudo-classes</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E::first-line</td>
        <td class="meaning">the first formatted line of an E element</td>
        <td class="described"><a
            href="#first-line">The ::first-line
            pseudo-element</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E::first-letter</td>
        <td class="meaning">the first formatted letter of an E element</td>
        <td class="described"><a
            href="#first-letter">The ::first-letter
            pseudo-element</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E::selection</td>
        <td class="meaning">the portion of an E element that is currently
            selected/highlighted by the user</td>
        <td class="described"><a
            href="#UIfragments">The UI element
            fragments pseudo-elements</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E::before</td>
        <td class="meaning">generated content before an E element</td>
        <td class="described"><a
            href="#gen-content">The ::before
            pseudo-element</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E::after</td>
        <td class="meaning">generated content after an E element</td>
        <td class="described"><a
            href="#gen-content">The ::after
            pseudo-element</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E.warning</td>
        <td class="meaning">an E element whose class is
            "warning" (the document language specifies how class is determined).</td>
        <td class="described"><a
            href="#class-html">Class
            selectors</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E#myid</td>
        <td class="meaning">an E element with ID equal to "myid".</td>
        <td class="described"><a
            href="#id-selectors">ID
            selectors</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E:not(s)</td>
        <td class="meaning">an E element that does not match simple selector s</td>
        <td class="described"><a
            href="#negation">Negation
            pseudo-class</a></td>
        <td class="origin">3</td></tr>
    <tr>
        <td class="pattern">E F</td>
        <td class="meaning">an F element descendant of an E element</td>
        <td class="described"><a
            href="#descendant-combinators">Descendant
            combinator</a></td>
        <td class="origin">1</td></tr>
    <tr>
        <td class="pattern">E &gt; F</td>
        <td class="meaning">an F element child of an E element</td>
        <td class="described"><a
            href="#child-combinators">Child
            combinator</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E + F</td>
        <td class="meaning">an F element immediately preceded by an E element</td>
        <td class="described"><a
            href="#adjacent-sibling-combinators">Adjacent sibling combinator</a></td>
        <td class="origin">2</td></tr>
    <tr>
        <td class="pattern">E ~ F</td>
        <td class="meaning">an F element preceded by an E element</td>
        <td class="described"><a
            href="#general-sibling-combinators">General sibling combinator</a></td>
        <td class="origin">3</td></tr></tbody></table>

<p>The meaning of each selector is derived from the table above by
    prepending "matches" to the contents of each cell in the "Meaning"
    column.</p>

<h2><a name=casesens>3. Case sensitivity</a></h2>

<p>The case sensitivity of document language element names, attribute
    names, and attribute values in selectors depends on the document
    language. For example, in HTML, element names are case-insensitive,
    but in XML, they are case-sensitive.</p>

<h2><a name=selector-syntax>4. Selector syntax</a></h2>

<p>A <dfn><a name=selector>selector</a></dfn> is a chain of one
    or more <a href="#sequence">sequences of simple selectors</a>
    separated by <a href="#combinators">combinators</a>.</p>

<p>A <dfn><a name=sequence>sequence of simple selectors</a></dfn>
    is a chain of <a href="#simple-selectors-dfn">simple selectors</a>
    that are not separated by a <a href="#combinators">combinator</a>. It
    always begins with a <a href="#type-selectors">type selector</a> or a
    <a href="#universal-selector">universal selector</a>. No other type
    selector or universal selector is allowed in the sequence.</p>

<p>A <dfn><a name=simple-selectors-dfn></a><a
    href="#simple-selectors">simple selector</a></dfn> is either a <a
    href="#type-selectors">type selector</a>, <a
    href="#universal-selector">universal selector</a>, <a
    href="#attribute-selectors">attribute selector</a>, <a
    href="#class-html">class selector</a>, <a
    href="#id-selectors">ID selector</a>, <a
    href="#content-selectors">content selector</a>, or <a
    href="#pseudo-classes">pseudo-class</a>. One <a
    href="#pseudo-elements">pseudo-element</a> may be appended to the last
    sequence of simple selectors.</p>

<p><dfn>Combinators</dfn> are: white space, &quot;greater-than
    sign&quot; (U+003E, <code>&gt;</code>), &quot;plus sign&quot; (U+002B,
    <code>+</code>) and &quot;tilde&quot; (U+007E, <code>~</code>).  White
    space may appear between a combinator and the simple selectors around
    it. <a name=whitespace></a>Only the characters "space" (U+0020), "tab"
    (U+0009), "line feed" (U+000A), "carriage return" (U+000D), and "form
    feed" (U+000C) can occur in white space. Other space-like characters,
    such as "em-space" (U+2003) and "ideographic space" (U+3000), are
    never part of white space.</p>

<p>The elements of a document tree that are represented by a selector
    are the <dfn><a name=subject></a>subjects of the selector</dfn>. A
    selector consisting of a single sequence of simple selectors
    represents any element satisfying its requirements. Prepending another
    sequence of simple selectors and a combinator to a sequence imposes
    additional matching constraints, so the subjects of a selector are
    always a subset of the elements represented by the last sequence of
    simple selectors.</p>

<p>An empty selector, containing no sequence of simple selectors and
    no pseudo-element, is an <a href="#Conformance">invalid
        selector</a>.</p>

<h2><a name=grouping>5. Groups of selectors</a></h2>

<p>When several selectors share the same declarations, they may be
    grouped into a comma-separated list. (A comma is U+002C.)</p>

<div class="example">
    <p>CSS examples:</p>
    <p>In this example, we condense three rules with identical
        declarations into one. Thus,</p>
    <pre>h1 { font-family: sans-serif }
h2 { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
    <p>is equivalent to:</p>
    <pre>h1, h2, h3 { font-family: sans-serif }</pre>
</div>

<p><strong>Warning</strong>: the equivalence is true in this example
    because all the selectors are valid selectors. If just one of these
    selectors were invalid, the entire group of selectors would be
    invalid. This would invalidate the rule for all three heading
    elements, whereas in the former case only one of the three individual
    heading rules would be invalidated.</p>


<h2><a name=simple-selectors>6. Simple selectors</a></h2>

<h3><a name=type-selectors>6.1. Type selector</a></h3>

<p>A <dfn>type selector</dfn> is the name of a document language
    element type. A type selector represents an instance of the element
    type in the document tree.</p>

<div class="example">
    <p>Example:</p>
    <p>The following selector represents an <code>h1</code> element in the document tree:</p>
    <pre>h1</pre>
</div>


<h4><a name=typenmsp>6.1.1. Type selectors and namespaces</a></h4>

<p>Type selectors allow an optional namespace (<a
    href="#refsXMLNAMES">[XMLNAMES]</a>) component. A namespace prefix
    that has been previously declared may be prepended to the element name
    separated by the namespace separator &quot;vertical bar&quot;
    (U+007C, <code>|</code>).</p>

<p>The namespace component may be left empty to indicate that the
    selector is only to represent elements with no declared namespace.</p>

<p>An asterisk may be used for the namespace prefix, indicating that
    the selector represents elements in any namespace (including elements
    with no namespace).</p>

<p>Element type selectors that have no namespace component (no
    namespace separator), represent elements without regard to the
    element's namespace (equivalent to "<code>*|</code>") unless a default
    namespace has been declared. If a default namespace has been declared,
    the selector will represent only elements in the default
    namespace.</p>

<p>A type selector containing a namespace prefix that has not been
    previously declared is an <a href="#Conformance">invalid</a> selector.
    The mechanism for declaring a namespace prefix is left up to the
    language implementing Selectors. In CSS, such a mechanism is defined
    in the General Syntax module.</p>

<p>In a namespace-aware client, element type selectors will only match
    against the <a
        href="http://www.w3.org/TR/REC-xml-names/#NT-LocalPart">local part</a>
    of the element's <a
        href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">qualified
        name</a>. See <a href="#downlevel">below</a> for notes about matching
    behaviors in down-level clients.</p>

<p>In summary:</p>

<dl>
    <dt><code>ns|E</code></dt>
    <dd>elements with name E in namespace ns</dd>
    <dt><code>*|E</code></dt>
    <dd>elements with name E in any namespace, including those without any
        declared namespace</dd>
    <dt><code>|E</code></dt>
    <dd>elements with name E without any declared namespace</dd>
    <dt><code>E</code></dt>
    <dd>if no default namespace has been specified, this is equivalent to *|E.
        Otherwise it is equivalent to ns|E where ns is the default namespace.</dd>
</dl>

<div class="example">
    <p>CSS examples:</p>

    <pre>@namespace foo url(http://www.example.com);
 foo|h1 { color: blue }
 foo|* { color: yellow }
 |h1 { color: red }
 *|h1 { color: green }
 h1 { color: green }</pre>

    <p>The first rule will match only <code>h1</code> elements in the
        "http://www.example.com" namespace.</p>

    <p>The second rule will match all elements in the
        "http://www.example.com" namespace.</p>

    <p>The third rule will match only <code>h1</code> elements without
        any declared namespace.</p>

    <p>The fourth rule will match <code>h1</code> elements in any
        namespace (including those without any declared namespace).</p>

    <p>The last rule is equivalent to the fourth rule because no default
        namespace has been defined.</p>

</div>

<h3><a name=universal-selector>6.2. Universal selector</a> </h3>

<p>The <dfn>universal selector</dfn>, written &quot;asterisk&quot;
    (<code>*</code>), represents the qualified name of any element
    type. It represents any single element in the document tree in any
    namespace (including those without any declared namespace) if no
    default namespace has been specified. If a default namespace has been
    specified, see <a href="#univnmsp">Universal selector and
        Namespaces</a> below.</p>

<p>If the universal selector is not the only component of a sequence
    of simple selectors, the <code>*</code> may be omitted.</p>

<div class="example">
    <p>Examples:</p>
    <ul>
        <li><code>*[hreflang|=en]</code> and <code>[hreflang|=en]</code> are equivalent,</li>
        <li><code>*.warning</code> and <code>.warning</code> are equivalent,</li>
        <li><code>*#myid</code> and <code>#myid</code> are equivalent.</li>
    </ul>
</div>

<p class="note"><strong>Note:</strong> it is recommended that the
    <code>*</code>, representing the universal selector, not be
    omitted.</p>

<h4><a name=univnmsp>6.2.1. Universal selector and namespaces</a></h4>

<p>The universal selector allows an optional namespace component. It
    is used as follows:</p>

<dl>
    <dt><code>ns|*</code></dt>
    <dd>all elements in namespace ns</dd>
    <dt><code>*|*</code></dt>
    <dd>all elements</dd>
    <dt><code>|*</code></dt>
    <dd>all elements without any declared namespace</dd>
    <dt><code>*</code></dt>
    <dd>if no default namespace has been specified, this is equivalent to *|*.
        Otherwise it is equivalent to ns|* where ns is the default namespace.</dd>
</dl>

<p>A universal selector containing a namespace prefix that has not
    been previously declared is an <a href="#Conformance">invalid</a>
    selector.  The mechanism for declaring a namespace prefix is left up
    to the language implementing Selectors.  In CSS, such a mechanism is
    defined in the General Syntax module.</p>


<h3><a name=attribute-selectors>6.3. Attribute selectors</a></h3>

<p>Selectors allow the representation of an element's attributes. When
    a selector is used as an expression to match against an element,
    attribute selectors must be considered to match an element if that
    element has an attribute that matches the attribute represented by the
    attribute selector.</p>

<h4><a name=attribute-representation>6.3.1. Attribute presence and values
    selectors</a></h4>

<p>CSS2 introduced four attribute selectors:</p>

<dl>
    <dt><code>[att]</code>
    <dd>Represents an element with the <code>att</code> attribute, whatever the value of
        the attribute.</dd>
    <dt><code>[att=val]</code></dt>
    <dd>Represents an element with the <code>att</code> attribute whose value is exactly
        "val".</dd>
    <dt><code>[att~=val]</code></dt>
    <dd>Represents an element with the <code>att</code> attribute whose value is a <a
        href="#whitespace">whitespace</a>-separated list of words, one of
        which is exactly "val". If "val" contains whitespace, it will never
        represent anything (since the words are <em>separated</em> by
        spaces).</dd>
    <dt><code>[att|=val]</code>
    <dd>Represents an element with the <code>att</code> attribute, its value either
        being exactly "val" or beginning with "val" immediately followed by
        "-" (U+002D).  This is primarily intended to allow language subcode
        matches (e.g., the <code>hreflang</code> attribute on the
        <code>link</code> element in HTML) as described in RFC 3066 (<a
            href="#refsRFC3066">[RFC3066]</a>).  For <code>lang</code> (or
        <code>xml:lang</code>) language subcode matching, please see <a
            href="#lang-pseudo">the <code>:lang</code> pseudo-class</a>.</dd>
</dl>

<p>Attribute values must be identifiers or strings. The
    case-sensitivity of attribute names and values in selectors depends on
    the document language.</p>

<div class="example">

    <p>Examples:</p>

    <p>The following attribute selector represents an <code>h1</code>
        element that carries the <code>title</code> attribute, whatever its
        value:</p>

    <pre>h1[title]</pre>

    <p>In the following example, the selector represents a
        <code>span</code> element whose <code>class</code> attribute has
        exactly the value "example":</p>

    <pre>span[class="example"]</pre>

    <p>Multiple attribute selectors can be used to represent several
        attributes of an element, or several conditions on the same
        attribute. Here, the selector represents a <code>span</code> element
        whose <code>hello</code> attribute has exactly the value "Cleveland"
        and whose <code>goodbye</code> attribute has exactly the value
        "Columbus":</p>

    <pre>span[hello="Cleveland"][goodbye="Columbus"]</pre>

    <p>The following selectors illustrate the differences between "="
        and "~=".  The first selector will represent, for example, the value
        "copyright copyleft copyeditor" on a <code>rel</code> attribute. The
        second selector will only represent an <code>a</code> element with
        an <code>href</code> attribute having the exact value
        "http://www.w3.org/".</p>

    <pre>a[rel~="copyright"]
a[href="http://www.w3.org/"]</pre>

    <p>The following selector represents a <code>link</code> element
        whose <code>hreflang</code> attribute is exactly "fr".</p>

    <pre>link[hreflang=fr]</pre>

    <p>The following selector represents a <code>link</code> element for
        which the values of the <code>hreflang</code> attribute begins with
        "en", including "en", "en-US", and "en-cockney":</p>

    <pre>link[hreflang|="en"]</pre>

    <p>Similarly, the following selectors represents a
        <code>DIALOGUE</code> element whenever it has one of two different
        values for an attribute <code>character</code>:</p>

    <pre>DIALOGUE[character=romeo]
DIALOGUE[character=juliet]</pre>

</div>

<h4><a name=attribute-substrings></a>6.3.2. Substring matching attribute
    selectors</h4>

<p>Three additional attribute selectors are provided for matching
    substrings in the value of an attribute:</p>

<dl>
    <dt><code>[att^=val]</code></dt>
    <dd>Represents an element with the <code>att</code> attribute whose value begins
        with the prefix "val".</dd>
    <dt><code>[att$=val]</code>
    <dd>Represents an element with the <code>att</code> attribute whose value ends with
        the suffix "val".</dd>
    <dt><code>[att*=val]</code>
    <dd>Represents an element with the <code>att</code> attribute whose value contains
        at least one instance of the substring "val".</dd>
</dl>

<p>Attribute values must be identifiers or strings. The
    case-sensitivity of attribute names in selectors depends on the
    document language.</p>

<div class="example">
    <p>Examples:</p>
    <p>The following selector represents an HTML <code>object</code>, referencing an
        image:</p>
    <pre>object[type^="image/"]</pre>
    <p>The following selector represents an HTML anchor <code>a</code> with an
        <code>href</code> attribute whose value ends with ".html".</p>
    <pre>a[href$=".html"]</pre>
    <p>The following selector represents an HTML paragraph with a <code>title</code>
        attribute whose value contains the substring "hello"</p>
    <pre>p[title*="hello"]</pre>
</div>

<h4><a name=attrnmsp>6.3.3. Attribute selectors and namespaces</a></h4>

<p>Attribute selectors allow an optional namespace component to the
    attribute name. A namespace prefix that has been previously declared
    may be prepended to the attribute name separated by the namespace
    separator &quot;vertical bar&quot; (<code>|</code>). In keeping with
    the Namespaces in the XML recommendation, default namespaces do not
    apply to attributes, therefore attribute selectors without a namespace
    component apply only to attributes that have no declared namespace
    (equivalent to "<code>|attr</code>"). An asterisk may be used for the
    namespace prefix indicating that the selector is to match all
    attribute names without regard to the attribute's namespace.

<p>An attribute selector with an attribute name containing a namespace
    prefix that has not been previously declared is an <a
        href="#Conformance">invalid</a> selector.  The mechanism for declaring
    a namespace prefix is left up to the language implementing Selectors.
    In CSS, such a mechanism is defined in the General Syntax module.

<div class="example">
    <p>CSS examples:</p>
    <pre>@namespace foo "http://www.example.com";
[foo|att=val] { color: blue }
[*|att] { color: yellow }
[|att] { color: green }
[att] { color: green }</pre>

    <p>The first rule will match only elements with the attribute
        <code>att</code> in the "http://www.example.com" namespace with the
        value "val".</p>

    <p>The second rule will match only elements with the attribute
        <code>att</code> regardless of the namespace of the attribute
        (including no declared namespace).</p>

    <p>The last two rules are equivalent and will match only elements
        with the attribute <code>att</code> where the attribute is not
        declared to be in a namespace.</p>

</div>

<h4><a name=def-values>6.3.4. Default attribute values in DTDs</a></h4>

<p>Attribute selectors represent explicitly set attribute values in
    the document tree. Default attribute values may be defined in a DTD or
    elsewhere, but cannot always be selected by attribute
    selectors. Selectors should be designed so that they work even if the
    default values are not included in the document tree.</p>

<p>More precisely, a UA is <em>not</em> required to read an "external
    subset" of the DTD but <em>is</em> required to look for default
    attribute values in the document's "internal subset." (See <a
        href="#refsXML10">[XML10]</a> for definitions of these subsets.)</p>

<p>A UA that recognizes an XML namespace <a
    href="#refsXMLNAMES">[XMLNAMES]</a> is not required to use its
    knowledge of that namespace to treat default attribute values as if
    they were present in the document. (For example, an XHTML UA is not
    required to use its built-in knowledge of the XHTML DTD.)</p>

<p class="note"><strong>Note:</strong> Typically, implementations
    choose to ignore external subsets.</p>

<div class="example">
    <p>Example:</p>

    <p>Consider an element EXAMPLE with an attribute "notation" that has a
        default value of "decimal". The DTD fragment might be</p>

    <pre class="dtd-example">&lt;!ATTLIST EXAMPLE notation (decimal,octal) "decimal"></pre>

    <p>If the style sheet contains the rules</p>

    <pre>EXAMPLE[notation=decimal] { /*... default property settings ...*/ }
EXAMPLE[notation=octal]   { /*... other settings...*/ }</pre>

    <p>the first rule will not match elements whose "notation" attribute
        is set by default, i.e. not set explicitly. To catch all cases, the
        attribute selector for the default value must be dropped:</p>

    <pre>EXAMPLE                   { /*... default property settings ...*/ }
EXAMPLE[notation=octal]   { /*... other settings...*/ }</pre>

    <p>Here, because the selector <code>EXAMPLE[notation=octal]</code> is
        more specific than the tag
        selector alone, the style declarations in the second rule will override
        those in the first for elements that have a "notation" attribute value
        of "octal". Care has to be taken that all property declarations that
        are to apply only to the default case are overridden in the non-default
        cases' style rules.</p>

</div>

<h3><a name=class-html>6.4. Class selectors</a></h3>

<p>Working with HTML, authors may use the period (U+002E,
    <code>.</code>) notation as an alternative to the <code>~=</code>
    notation when representing the <code>class</code> attribute. Thus, for
    HTML, <code>div.value</code> and <code>div[class~=value]</code> have
    the same meaning. The attribute value must immediately follow the
    &quot;period&quot; (<code>.</code>).</p>

<p>UAs may apply selectors using the period (.) notation in XML
    documents if the UA has namespace-specific knowledge that allows it to
    determine which attribute is the &quot;class&quot; attribute for the
    respective namespace. One such example of namespace-specific knowledge
    is the prose in the specification for a particular namespace (e.g. SVG
    1.0 <a href="#refsSVG">[SVG]</a> describes the <a
        href="http://www.w3.org/TR/2001/PR-SVG-20010719/styling.html#ClassAttribute">SVG
        &quot;class&quot; attribute</a> and how a UA should interpret it, and
    similarly MathML 1.01 <a href="#refsMATH">[MATH]</a> describes the <a
        href="http://www.w3.org/1999/07/REC-MathML-19990707/chapter2.html#sec2.3.4">MathML
        &quot;class&quot; attribute</a>.)</p>

<div class="example">
    <p>CSS examples:</p>

    <p>We can assign style information to all elements with
        <code>class~="pastoral"</code> as follows:</p>

    <pre>*.pastoral { color: green }  /* all elements with class~=pastoral */</pre>

    <p>or just</p>

    <pre>.pastoral { color: green }  /* all elements with class~=pastoral */</pre>

    <p>The following assigns style only to H1 elements with
        <code>class~="pastoral"</code>:</p>

    <pre>H1.pastoral { color: green }  /* H1 elements with class~=pastoral */</pre>

    <p>Given these rules, the first H1 instance below would not have
        green text, while the second would:</p>

    <pre>&lt;H1&gt;Not green&lt;/H1&gt;
&lt;H1 class="pastoral"&gt;Very green&lt;/H1&gt;</pre>

</div>

<p>To represent a subset of "class" values, each value must be preceded
    by a ".", in any order.</P>

<div class="example">

    <p>CSS example:</p>

    <p>The following rule matches any P element whose "class" attribute
        has been assigned a list of <a
            href="#whitespace">whitespace</a>-separated values that includes
        "pastoral" and "marine":</p>

    <pre>p.pastoral.marine { color: green }</pre>

    <p>This rule matches when <code>class="pastoral blue aqua
        marine"</code> but does not match for <code>class="pastoral
        blue"</code>.</p>

</div>

<p class="note"><strong>Note:</strong> Because CSS gives considerable
    power to the "class" attribute, authors could conceivably design their
    own "document language" based on elements with almost no associated
    presentation (such as DIV and SPAN in HTML) and assigning style
    information through the "class" attribute.  Authors should avoid this
    practice since the structural elements of a document language often
    have recognized and accepted meanings and author-defined classes may
    not.</p>

<p class="note"><strong>Note:</strong> If an element has multiple
    class attributes, their values must be concatenated with spaces
    between the values before searching for the class. As of this time the
    working group is not aware of any manner in which this situation can
    be reached, however, so this behavior is explicitly non-normative in
    this specification.</p>

<h3><a name=id-selectors>6.5. ID selectors</a></h3>

<p>Document languages may contain attributes that are declared to be
    of type ID. What makes attributes of type ID special is that no two
    such attributes can have the same value in a document, regardless of
    the type of the elements that carry them; whatever the document
    language, an ID typed attribute can be used to uniquely identify its
    element. In HTML all ID attributes are named "id"; XML applications
    may name ID attributes differently, but the same restriction
    applies.</p>

<p>An ID-typed attribute of a document language allows authors to
    assign an identifier to one element instance in the document tree. W3C
    ID selectors represent an element instance based on its identifier. An
    ID selector contains a &quot;number sign&quot; (U+0023,
    <code>#</code>) immediately followed by the ID value, which must be an
    identifier.</p>

<p>Selectors does not specify how a UA knows the ID-typed attribute of
    an element. The UA may, e.g., read a document's DTD, have the
    information hard-coded or ask the user.

<div class="example">
    <p>Examples:</p>
    <p>The following ID selector represents an <code>h1</code> element
        whose ID-typed attribute has the value "chapter1":</p>
    <pre>h1#chapter1</pre>
    <p>The following ID selector represents any element whose ID-typed
        attribute has the value "chapter1":</p>
    <pre>#chapter1</pre>
    <p>The following selector represents any element whose ID-typed
        attribute has the value "z98y".</p>
    <pre>*#z98y</pre>
</div>

<p class="note"><strong>Note.</strong> In XML 1.0 <a
    href="#refsXML10">[XML10]</a>, the information about which attribute
    contains an element's IDs is contained in a DTD or a schema. When
    parsing XML, UAs do not always read the DTD, and thus may not know
    what the ID of an element is (though a UA may have namespace-specific
    knowledge that allows it to determine which attribute is the ID
    attribute for that namespace). If a style sheet designer knows or
    suspects that a UA may not know what the ID of an element is, he
    should use normal attribute selectors instead:
    <code>[name=p371]</code> instead of <code>#p371</code>.  Elements in
    XML 1.0 documents without a DTD do not have IDs at all.</p>

<p>If an element has multiple ID attributes, all of them must be
    treated as IDs for that element for the purposes of the ID
    selector. Such a situation could be reached using mixtures of xml:id,
    DOM3 Core, XML DTDs, and namespace-specific knowledge.</p>

<h3><a name=pseudo-classes>6.6. Pseudo-classes</a></h3>

<p>The pseudo-class concept is introduced to permit selection based on
    information that lies outside of the document tree or that cannot be
    expressed using the other simple selectors.</p>

<p>A pseudo-class always consists of a &quot;colon&quot;
    (<code>:</code>) followed by the name of the pseudo-class and
    optionally by a value between parentheses.</p>

<p>Pseudo-classes are allowed in all sequences of simple selectors
    contained in a selector. Pseudo-classes are allowed anywhere in
    sequences of simple selectors, after the leading type selector or
    universal selector (possibly omitted). Pseudo-class names are
    case-insensitive. Some pseudo-classes are mutually exclusive, while
    others can be applied simultaneously to the same
    element. Pseudo-classes may be dynamic, in the sense that an element
    may acquire or lose a pseudo-class while a user interacts with the
    document.</p>


<h4><a name=dynamic-pseudos>6.6.1. Dynamic pseudo-classes</a></h4>

<p>Dynamic pseudo-classes classify elements on characteristics other
    than their name, attributes, or content, in principle characteristics
    that cannot be deduced from the document tree.</p>

<p>Dynamic pseudo-classes do not appear in the document source or
    document tree.</p>


<h5>The <a name=link>link pseudo-classes: :link and :visited</a></h5>

<p>User agents commonly display unvisited links differently from
    previously visited ones. Selectors
    provides the pseudo-classes <code>:link</code> and
    <code>:visited</code> to distinguish them:</p>

<ul>
    <li>The <code>:link</code> pseudo-class applies to links that have
        not yet been visited.</li>
    <li>The <code>:visited</code> pseudo-class applies once the link has
        been visited by the user. </li>
</ul>

<p>After some amount of time, user agents may choose to return a
    visited link to the (unvisited) ':link' state.</p>

<p>The two states are mutually exclusive.</p>

<div class="example">

    <p>Example:</p>

    <p>The following selector represents links carrying class
        <code>external</code> and already visited:</p>

    <pre>a.external:visited</pre>

</div>

<p class="note"><strong>Note:</strong> It is possible for style sheet
    authors to abuse the :link and :visited pseudo-classes to determine
    which sites a user has visited without the user's consent.

<p>UAs may therefore treat all links as unvisited links, or implement
    other measures to preserve the user's privacy while rendering visited
    and unvisited links differently.</p>

<h5>The <a name=useraction-pseudos>user action pseudo-classes
    :hover, :active, and :focus</a></h5>

<p>Interactive user agents sometimes change the rendering in response
    to user actions. Selectors provides
    three pseudo-classes for the selection of an element the user is
    acting on.</p>

<ul>

    <li>The <code>:hover</code> pseudo-class applies while the user
        designates an element with a pointing device, but does not activate
        it. For example, a visual user agent could apply this pseudo-class
        when the cursor (mouse pointer) hovers over a box generated by the
        element. User agents not that do not support <a
            href="http://www.w3.org/TR/REC-CSS2/media.html#interactive-media-group">interactive
            media</a> do not have to support this pseudo-class. Some conforming
        user agents that support <a
            href="http://www.w3.org/TR/REC-CSS2/media.html#interactive-media-group">interactive
            media</a> may not be able to support this pseudo-class (e.g., a pen
        device that does not detect hovering).</li>

    <li>The <code>:active</code> pseudo-class applies while an element
        is being activated by the user. For example, between the times the
        user presses the mouse button and releases it.</li>

    <li>The <code>:focus</code> pseudo-class applies while an element
        has the focus (accepts keyboard or mouse events, or other forms of
        input). </li>

</ul>

<p>There may be document language or implementation specific limits on
    which elements can become <code>:active</code> or acquire
    <code>:focus</code>.</p>

<p>These pseudo-classes are not mutually exclusive. An element may
    match several pseudo-classes at the same time.</p>

<p>Selectors doesn't define if the parent of an element that is
    ':active' or ':hover' is also in that state.</p>

<div class="example">
    <p>Examples:</p>
    <pre>a:link    /* unvisited links */
a:visited /* visited links */
a:hover   /* user hovers */
a:active  /* active links */</pre>
    <p>An example of combining dynamic pseudo-classes:</p>
    <pre>a:focus
a:focus:hover</pre>
    <p>The last selector matches <code>a</code> elements that are in
        the pseudo-class :focus and in the pseudo-class :hover.</p>
</div>

<p class="note"><strong>Note:</strong> An element can be both ':visited'
    and ':active' (or ':link' and ':active').</p>

<h4><a name=target-pseudo>6.6.2. The target pseudo-class :target</a></h4>

<p>Some URIs refer to a location within a resource. This kind of URI
    ends with a &quot;number sign&quot; (#) followed by an anchor
    identifier (called the fragment identifier).</p>

<p>URIs with fragment identifiers link to a certain element within the
    document, known as the target element. For instance, here is a URI
    pointing to an anchor named <code>section_2</code> in an HTML
    document:</p>

<pre>http://example.com/html/top.html#section_2</pre>

<p>A target element can be represented by the <code>:target</code>
    pseudo-class. If the document's URI has no fragment identifier, then
    the document has no target element.</p>

<div class="example">
    <p>Example:</p>
    <pre>p.note:target</pre>
    <p>This selector represents a <code>p</code> element of class
        <code>note</code> that is the target element of the referring
        URI.</p>
</div>

<div class="example">
    <p>CSS example:</p>
    <p>Here, the <code>:target</code> pseudo-class is used to make the
        target element red and place an image before it, if there is one:</p>
    <pre>*:target { color : red }
*:target::before { content : url(target.png) }</pre>
</div>

<h4><a name=lang-pseudo>6.6.3. The language pseudo-class :lang</a></h4>

<p>If the document language specifies how the human language of an
    element is determined, it is possible to write selectors that
    represent an element based on its language. For example, in HTML <a
        href="#refsHTML4">[HTML4]</a>, the language is determined by a
    combination of the <code>lang</code> attribute, the <code>meta</code>
    element, and possibly by information from the protocol (such as HTTP
    headers). XML uses an attribute called <code>xml:lang</code>, and
    there may be other document language-specific methods for determining
    the language.</p>

<p>The pseudo-class <code>:lang(C)</code> represents an element that
    is in language C. Whether an element is represented by a
    <code>:lang()</code> selector is based solely on the identifier C
    being either equal to, or a hyphen-separated substring of, the
    element's language value, in the same way as if performed by the <a
        href="#attribute-representation">'|='</a> operator in attribute
    selectors. The identifier C does not have to be a valid language
    name.</p>

<p>C must not be empty. (If it is, the selector is invalid.)</p>

<p class="note"><strong>Note:</strong> It is recommended that
    documents and protocols indicate language using codes from RFC 3066 <a
        href="#refsRFC3066">[RFC3066]</a> or its successor, and by means of
    "xml:lang" attributes in the case of XML-based documents <a
        href="#refsXML10">[XML10]</a>. See <a
        href="http://www.w3.org/International/questions/qa-lang-2or3.html">
        "FAQ: Two-letter or three-letter language codes."</a></p>

<div class="example">
    <p>Examples:</p>
    <p>The two following selectors represent an HTML document that is in
        Belgian, French, or German. The two next selectors represent
        <code>q</code> quotations in an arbitrary element in Belgian, French,
        or German.</p>
    <pre>html:lang(fr-be)
html:lang(de)
:lang(fr-be) &gt; q
:lang(de) &gt; q</pre>
</div>

<h4><a name=UIstates>6.6.4. The UI element states pseudo-classes</a></h4>

<h5><a name=enableddisabled>The :enabled and :disabled pseudo-classes</a></h5>

<p>The <code>:enabled</code> pseudo-class allows authors to customize
    the look of user interface elements that are enabled &mdash; which the
    user can select or activate in some fashion (e.g. clicking on a button
    with a mouse).  There is a need for such a pseudo-class because there
    is no way to programmatically specify the default appearance of say,
    an enabled <code>input</code> element without also specifying what it
    would look like when it was disabled.</p>

<p>Similar to <code>:enabled</code>, <code>:disabled</code> allows the
    author to specify precisely how a disabled or inactive user interface
    element should look.</p>

<p>Most elements will be neither enabled nor disabled.  An element is
    enabled if the user can either activate it or transfer the focus to
    it. An element is disabled if it could be enabled, but the user cannot
    presently activate it or transfer focus to it.</p>


<h5><a name=checked>The :checked pseudo-class</a></h5>

<p>Radio and checkbox elements can be toggled by the user. Some menu
    items are "checked" when the user selects them. When such elements are
    toggled "on" the <code>:checked</code> pseudo-class applies. The
    <code>:checked</code> pseudo-class initially applies to such elements
    that have the HTML4 <code>selected</code> and <code>checked</code>
    attributes as described in <a
        href="http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.2.1">Section
        17.2.1 of HTML4</a>, but of course the user can toggle "off" such
    elements in which case the <code>:checked</code> pseudo-class would no
    longer apply. While the <code>:checked</code> pseudo-class is dynamic
    in nature, and is altered by user action, since it can also be based
    on the presence of the semantic HTML4 <code>selected</code> and
    <code>checked</code> attributes, it applies to all media.


<h5><a name=indeterminate>The :indeterminate pseudo-class</a></h5>

<div class="note">

    <p>Radio and checkbox elements can be toggled by the user, but are
        sometimes in an indeterminate state, neither checked nor unchecked.
        This can be due to an element attribute, or DOM manipulation.</p>

    <p>A future version of this specification may introduce an
        <code>:indeterminate</code> pseudo-class that applies to such elements.
        <!--While the <code>:indeterminate</code> pseudo-class is dynamic in
        nature, and is altered by user action, since it can also be based on
        the presence of an element attribute, it applies to all media.</p>

        <p>Components of a radio-group initialized with no pre-selected choice
        are an example of :indeterminate state.--></p>

</div>


<h4><a name=structural-pseudos>6.6.5. Structural pseudo-classes</a></h4>

<p>Selectors introduces the concept of <dfn>structural
    pseudo-classes</dfn> to permit selection based on extra information that lies in
    the document tree but cannot be represented by other simple selectors or
    combinators.

<p>Note that standalone pieces of PCDATA (text nodes in the DOM) are
    not counted when calculating the position of an element in the list of
    children of its parent. When calculating the position of an element in
    the list of children of its parent, the index numbering starts at 1.


<h5><a name=root-pseudo>:root pseudo-class</a></h5>

<p>The <code>:root</code> pseudo-class represents an element that is
    the root of the document. In HTML 4, this is always the
    <code>HTML</code> element.


<h5><a name=nth-child-pseudo>:nth-child() pseudo-class</a></h5>

<p>The
    <code>:nth-child(<var>a</var><code>n</code>+<var>b</var>)</code>
    pseudo-class notation represents an element that has
    <var>a</var><code>n</code>+<var>b</var>-1 siblings
    <strong>before</strong> it in the document tree, for a given positive
    integer or zero value of <code>n</code>, and has a parent element. In
    other words, this matches the <var>b</var>th child of an element after
    all the children have been split into groups of <var>a</var> elements
    each. For example, this allows the selectors to address every other
    row in a table, and could be used to alternate the color
    of paragraph text in a cycle of four. The <var>a</var> and
    <var>b</var> values must be zero, negative integers or positive
    integers. The index of the first child of an element is 1.

<p>In addition to this, <code>:nth-child()</code> can take
    '<code>odd</code>' and '<code>even</code>' as arguments instead.
    '<code>odd</code>' has the same signification as <code>2n+1</code>,
    and '<code>even</code>' has the same signification as <code>2n</code>.


<div class="example">
    <p>Examples:</p>
    <pre>tr:nth-child(2n+1) /* represents every odd row of an HTML table */
tr:nth-child(odd)  /* same */
tr:nth-child(2n)   /* represents every even row of an HTML table */
tr:nth-child(even) /* same */

/* Alternate paragraph colours in CSS */
p:nth-child(4n+1) { color: navy; }
p:nth-child(4n+2) { color: green; }
p:nth-child(4n+3) { color: maroon; }
p:nth-child(4n+4) { color: purple; }</pre>
</div>

<p>When <var>a</var>=0, no repeating is used, so for example
    <code>:nth-child(0n+5)</code> matches only the fifth child. When
    <var>a</var>=0, the <var>a</var><code>n</code> part need not be
    included, so the syntax simplifies to
    <code>:nth-child(<var>b</var>)</code> and the last example simplifies
    to <code>:nth-child(5)</code>.

<div class="example">
    <p>Examples:</p>
    <pre>foo:nth-child(0n+1)   /* represents an element foo, first child of its parent element */
foo:nth-child(1)      /* same */</pre>
</div>

<p>When <var>a</var>=1, the number may be omitted from the rule.

<div class="example">
    <p>Examples:</p>
    <p>The following selectors are therefore equivalent:</p>
    <pre>bar:nth-child(1n+0)   /* represents all bar elements, specificity (0,1,1) */
bar:nth-child(n+0)    /* same */
bar:nth-child(n)      /* same */
bar                   /* same but lower specificity (0,0,1) */</pre>
</div>

<p>If <var>b</var>=0, then every <var>a</var>th element is picked. In
    such a case, the <var>b</var> part may be omitted.

<div class="example">
    <p>Examples:</p>
    <pre>tr:nth-child(2n+0) /* represents every even row of an HTML table */
tr:nth-child(2n) /* same */</pre>
</div>

<p>If both <var>a</var> and <var>b</var> are equal to zero, the
    pseudo-class represents no element in the document tree.</p>

<p>The value <var>a</var> can be negative, but only the positive
    values of <var>a</var><code>n</code>+<var>b</var>, for
    <code>n</code>&ge;0, may represent an element in the document
    tree.</p>

<div class="example">
    <p>Example:</p>
    <pre>html|tr:nth-child(-n+6)  /* represents the 6 first rows of XHTML tables */</pre>
</div>

<p>When the value <var>b</var> is negative, the "+" character in the
    expression must be removed (it is effectively replaced by the "-"
    character indicating the negative value of <var>b</var>).</p>

<div class="example">
    <p>Examples:</p>
    <pre>:nth-child(10n-1)  /* represents the 9th, 19th, 29th, etc, element */
:nth-child(10n+9)  /* Same */
:nth-child(10n+-1) /* Syntactically invalid, and would be ignored */</pre>
</div>


<h5><a name=nth-last-child-pseudo>:nth-last-child() pseudo-class</a></h5>

<p>The <code>:nth-last-child(<var>a</var>n+<var>b</var>)</code>
    pseudo-class notation represents an element that has
    <var>a</var><code>n</code>+<var>b</var>-1 siblings
    <strong>after</strong> it in the document tree, for a given positive
    integer or zero value of <code>n</code>, and has a parent element. See
    <code>:nth-child()</code> pseudo-class for the syntax of its argument.
    It also accepts the '<code>even</code>' and '<code>odd</code>' values
    as arguments.


<div class="example">
    <p>Examples:</p>
    <pre>tr:nth-last-child(-n+2)    /* represents the two last rows of an HTML table */

foo:nth-last-child(odd)    /* represents all odd foo elements in their parent element,
                              counting from the last one */</pre>
</div>


<h5><a name=nth-of-type-pseudo>:nth-of-type() pseudo-class</a></h5>

<p>The <code>:nth-of-type(<var>a</var>n+<var>b</var>)</code>
    pseudo-class notation represents an element that has
    <var>a</var><code>n</code>+<var>b</var>-1 siblings with the same
    element name <strong>before</strong> it in the document tree, for a
    given zero or positive integer value of <code>n</code>, and has a
    parent element. In other words, this matches the <var>b</var>th child
    of that type after all the children of that type have been split into
    groups of a elements each. See <code>:nth-child()</code> pseudo-class
    for the syntax of its argument. It also accepts the
    '<code>even</code>' and '<code>odd</code>' values.


<div class="example">
    <p>CSS example:</p>
    <p>This allows an author to alternate the position of floated images:</p>
    <pre>img:nth-of-type(2n+1) { float: right; }
img:nth-of-type(2n) { float: left; }</pre>
</div>


<h5><a name=nth-last-of-type-pseudo>:nth-last-of-type() pseudo-class</a></h5>

<p>The <code>:nth-last-of-type(<var>a</var>n+<var>b</var>)</code>
    pseudo-class notation represents an element that has
    <var>a</var><code>n</code>+<var>b</var>-1 siblings with the same
    element name <strong>after</strong> it in the document tree, for a
    given zero or positive integer value of <code>n</code>, and has a
    parent element. See <code>:nth-child()</code> pseudo-class for the
    syntax of its argument. It also accepts the '<code>even</code>' and '<code>odd</code>' values.


<div class="example">
    <p>Example:</p>
    <p>To represent all <code>h2</code> children of an XHTML
        <code>body</code> except the first and last, one could use the
        following selector:</p>
    <pre>body &gt; h2:nth-of-type(n+2):nth-last-of-type(n+2)</pre>
    <p>In this case, one could also use <code>:not()</code>, although the
        selector ends up being just as long:</p>
    <pre>body &gt; h2:not(:first-of-type):not(:last-of-type)</pre>
</div>


<h5><a name=first-child-pseudo>:first-child pseudo-class</a></h5>

<p>Same as <code>:nth-child(1)</code>. The <code>:first-child</code> pseudo-class
    represents an element that is the first child of some other element.


<div class="example">
    <p>Examples:</p>
    <p>The following selector represents a <code>p</code> element that is
        the first child of a <code>div</code> element:</p>
    <pre>div &gt; p:first-child</pre>
    <p>This selector can represent the <code>p</code> inside the
        <code>div</code> of the following fragment:</p>
    <pre>&lt;p&gt; The last P before the note.&lt;/p&gt;
&lt;div class="note"&gt;
   &lt;p&gt; The first P inside the note.&lt;/p&gt;
&lt;/div&gt;</pre>but cannot represent the second <code>p</code> in the following
    fragment:
    <pre>&lt;p&gt; The last P before the note.&lt;/p&gt;
&lt;div class="note"&gt;
   &lt;h2&gt; Note &lt;/h2&gt;
   &lt;p&gt; The first P inside the note.&lt;/p&gt;
&lt;/div&gt;</pre>
    <p>The following two selectors are usually equivalent:</p>
    <pre>* &gt; a:first-child /* a is first child of any element */
a:first-child /* Same (assuming a is not the root element) */</pre>
</div>

<h5><a name=last-child-pseudo>:last-child pseudo-class</a></h5>

<p>Same as <code>:nth-last-child(1)</code>. The <code>:last-child</code> pseudo-class
    represents an element that is the last child of some other element.

<div class="example">
    <p>Example:</p>
    <p>The following selector represents a list item <code>li</code> that
        is the last child of an ordered list <code>ol</code>.
    <pre>ol &gt; li:last-child</pre>
</div>

<h5><a name=first-of-type-pseudo>:first-of-type pseudo-class</a></h5>

<p>Same as <code>:nth-of-type(1)</code>. The <code>:first-of-type</code> pseudo-class
    represents an element that is the first sibling of its type in the list of
    children of its parent element.

<div class="example">
    <p>Example:</p>
    <p>The following selector represents a definition title
        <code>dt</code> inside a definition list <code>dl</code>, this
        <code>dt</code> being the first of its type in the list of children of
        its parent element.</p>
    <pre>dl dt:first-of-type</pre>
    <p>It is a valid description for the first two <code>dt</code>
        elements in the following example but not for the third one:</p>
    <pre>&lt;dl&gt;
 &lt;dt&gt;gigogne&lt;/dt&gt;
 &lt;dd&gt;
  &lt;dl&gt;
   &lt;dt&gt;fus&eacute;e&lt;/dt&gt;
   &lt;dd&gt;multistage rocket&lt;/dd&gt;
   &lt;dt&gt;table&lt;/dt&gt;
   &lt;dd&gt;nest of tables&lt;/dd&gt;
  &lt;/dl&gt;
 &lt;/dd&gt;
&lt;/dl&gt;</pre>
</div>

<h5><a name=last-of-type-pseudo>:last-of-type pseudo-class</a></h5>

<p>Same as <code>:nth-last-of-type(1)</code>. The
    <code>:last-of-type</code> pseudo-class represents an element that is
    the last sibling of its type in the list of children of its parent
    element.</p>

<div class="example">
    <p>Example:</p>
    <p>The following selector represents the last data cell
        <code>td</code> of a table row.</p>
    <pre>tr &gt; td:last-of-type</pre>
</div>

<h5><a name=only-child-pseudo>:only-child pseudo-class</a></h5>

<p>Represents an element that has a parent element and whose parent
    element has no other element children. Same as
    <code>:first-child:last-child</code> or
    <code>:nth-child(1):nth-last-child(1)</code>, but with a lower
    specificity.</p>

<h5><a name=only-of-type-pseudo>:only-of-type pseudo-class</a></h5>

<p>Represents an element that has a parent element and whose parent
    element has no other element children with the same element name. Same
    as <code>:first-of-type:last-of-type</code> or
    <code>:nth-of-type(1):nth-last-of-type(1)</code>, but with a lower
    specificity.</p>


<h5><a name=empty-pseudo></a>:empty pseudo-class</h5>

<p>The <code>:empty</code> pseudo-class represents an element that has
    no children at all. In terms of the DOM, only element nodes and text
    nodes (including CDATA nodes and entity references) whose data has a
    non-zero length must be considered as affecting emptiness; comments,
    PIs, and other nodes must not affect whether an element is considered
    empty or not.</p>

<div class="example">
    <p>Examples:</p>
    <p><code>p:empty</code> is a valid representation of the following fragment:</p>
    <pre>&lt;p&gt;&lt;/p&gt;</pre>
    <p><code>foo:empty</code> is not a valid representation for the
        following fragments:</p>
    <pre>&lt;foo&gt;bar&lt;/foo&gt;</pre>
    <pre>&lt;foo&gt;&lt;bar&gt;bla&lt;/bar&gt;&lt;/foo&gt;</pre>
    <pre>&lt;foo&gt;this is not &lt;bar&gt;:empty&lt;/bar&gt;&lt;/foo&gt;</pre>
</div>

<h4><a name=content-selectors>6.6.6. Blank</a></h4> <!-- It's the Return of Appendix H!!! Run away! -->

<p>This section intentionally left blank.</p>
<!-- (used to be :contains()) -->

<h4><a name=negation></a>6.6.7. The negation pseudo-class</h4>

<p>The negation pseudo-class, <code>:not(<var>X</var>)</code>, is a
    functional notation taking a <a href="#simple-selectors-dfn">simple
        selector</a> (excluding the negation pseudo-class itself and
    pseudo-elements) as an argument. It represents an element that is not
    represented by the argument.

    <!-- pseudo-elements are not simple selectors, so the above paragraph
    may be a bit confusing -->

<div class="example">
    <p>Examples:</p>
    <p>The following CSS selector matches all <code>button</code>
        elements in an HTML document that are not disabled.</p>
    <pre>button:not([DISABLED])</pre>
    <p>The following selector represents all but <code>FOO</code>
        elements.</p>
    <pre>*:not(FOO)</pre>
    <p>The following group of selectors represents all HTML elements
        except links.</p>
    <pre>html|*:not(:link):not(:visited)</pre>
</div>

<p>Default namespace declarations do not affect the argument of the
    negation pseudo-class unless the argument is a universal selector or a
    type selector.</p>

<div class="example">
    <p>Examples:</p>
    <p>Assuming that the default namespace is bound to
        "http://example.com/", the following selector represents all
        elements that are not in that namespace:</p>
    <pre>*|*:not(*)</pre>
    <p>The following CSS selector matches any element being hovered,
        regardless of its namespace. In particular, it is not limited to
        only matching elements in the default namespace that are not being
        hovered, and elements not in the default namespace don't match the
        rule when they <em>are</em> being hovered.</p>
    <pre>*|*:not(:hover)</pre>
</div>

<p class="note"><strong>Note</strong>: the :not() pseudo allows
    useless selectors to be written.  For instance <code>:not(*|*)</code>,
    which represents no element at all, or <code>foo:not(bar)</code>,
    which is equivalent to <code>foo</code> but with a higher
    specificity.</p>

<h3><a name=pseudo-elements>7. Pseudo-elements</a></h3>

<p>Pseudo-elements create abstractions about the document tree beyond
    those specified by the document language. For instance, document
    languages do not offer mechanisms to access the first letter or first
    line of an element's content. Pseudo-elements allow designers to refer
    to this otherwise inaccessible information. Pseudo-elements may also
    provide designers a way to refer to content that does not exist in the
    source document (e.g., the <code>::before</code> and
    <code>::after</code> pseudo-elements give access to generated
    content).</p>

<p>A pseudo-element is made of two colons (<code>::</code>) followed
    by the name of the pseudo-element.</p>

<p>This <code>::</code> notation is introduced by the current document
    in order to establish a discrimination between pseudo-classes and
    pseudo-elements.  For compatibility with existing style sheets, user
    agents must also accept the previous one-colon notation for
    pseudo-elements introduced in CSS levels 1 and 2 (namely,
    <code>:first-line</code>, <code>:first-letter</code>,
    <code>:before</code> and <code>:after</code>). This compatibility is
    not allowed for the new pseudo-elements introduced in CSS level 3.</p>

<p>Only one pseudo-element may appear per selector, and if present it
    must appear after the sequence of simple selectors that represents the
    <a href="#subject">subjects</a> of the selector. <span class="note">A
future version of this specification may allow multiple
pesudo-elements per selector.</span></p>

<h4><a name=first-line>7.1. The ::first-line pseudo-element</a></h4>

<p>The <code>::first-line</code> pseudo-element describes the contents
    of the first formatted line of an element.

<div class="example">
    <p>CSS example:</p>
    <pre>p::first-line { text-transform: uppercase }</pre>
    <p>The above rule means "change the letters of the first line of every
        paragraph to uppercase".</p>
</div>

<p>The selector <code>p::first-line</code> does not match any real
    HTML element. It does match a pseudo-element that conforming user
    agents will insert at the beginning of every paragraph.</p>

<p>Note that the length of the first line depends on a number of
    factors, including the width of the page, the font size, etc.  Thus,
    an ordinary HTML paragraph such as:</p>

<pre>
&lt;P&gt;This is a somewhat long HTML
paragraph that will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/P&gt;
</pre>

<p>the lines of which happen to be broken as follows:

<pre>
THIS IS A SOMEWHAT LONG HTML PARAGRAPH THAT
will be broken into several lines. The first
line will be identified by a fictional tag
sequence. The other lines will be treated as
ordinary lines in the paragraph.
</pre>

<p>This paragraph might be "rewritten" by user agents to include the
    <em>fictional tag sequence</em> for <code>::first-line</code>. This
    fictional tag sequence helps to show how properties are inherited.</p>

<pre>
&lt;P&gt;<b>&lt;P::first-line&gt;</b> This is a somewhat long HTML
paragraph that <b>&lt;/P::first-line&gt;</b> will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/P&gt;
</pre>

<p>If a pseudo-element breaks up a real element, the desired effect
    can often be described by a fictional tag sequence that closes and
    then re-opens the element. Thus, if we mark up the previous paragraph
    with a <code>span</code> element:</p>

<pre>
&lt;P&gt;<b>&lt;SPAN class="test"&gt;</b> This is a somewhat long HTML
paragraph that will be broken into several
lines.<b>&lt;/SPAN&gt;</b> The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/P&gt;
</pre>

<p>the user agent could simulate start and end tags for
    <code>span</code> when inserting the fictional tag sequence for
    <code>::first-line</code>.

<pre>
&lt;P&gt;&lt;P::first-line&gt;<b>&lt;SPAN class="test"&gt;</b> This is a
somewhat long HTML
paragraph that will <b>&lt;/SPAN&gt;</b>&lt;/P::first-line&gt;<b>&lt;SPAN class="test"&gt;</b> be
broken into several
lines.<b>&lt;/SPAN&gt;</b> The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/P&gt;
</pre>

<p>In CSS, the <code>::first-line</code> pseudo-element can only be
    attached to a block-level element, an inline-block, a table-caption,
    or a table-cell.</p>

<p><a name="first-formatted-line"></a>The "first formatted line" of an
    element may occur inside a
    block-level descendant in the same flow (i.e., a block-level
    descendant that is not positioned and not a float). E.g., the first
    line of the <code>div</code> in <code>&lt;DIV>&lt;P>This
        line...&lt;/P>&lt/DIV></code> is the first line of the <code>p</code> (assuming
    that both <code>p</code> and <code>div</code> are block-level).

<p>The first line of a table-cell or inline-block cannot be the first
    formatted line of an ancestor element. Thus, in <code>&lt;DIV&gt;&lt;P
        STYLE="display: inline-block">Hello&lt;BR&gt;Goodbye&lt;/P&gt;
        etcetera&lt;/DIV&gt;</code> the first formatted line of the
    <code>div</code> is not the line "Hello".

<p class="note">Note that the first line of the <code>p</code> in this
    fragment: <code>&lt;p&gt&lt;br&gt;First...</code> doesn't contain any
    letters (assuming the default style for <code>br</code> in HTML
    4). The word "First" is not on the first formatted line.

<p>A UA should act as if the fictional start tags of the
    <code>::first-line</code> pseudo-elements were nested just inside the
    innermost enclosing block-level element. (Since CSS1 and CSS2 were
    silent on this case, authors should not rely on this behavior.) Here
    is an example. The fictional tag sequence for</p>

<pre>
&lt;DIV>
  &lt;P>First paragraph&lt;/P>
  &lt;P>Second paragraph&lt;/P>
&lt;/DIV>
</pre>

<p>is</p>

<pre>
&lt;DIV>
  &lt;P>&lt;DIV::first-line>&lt;P::first-line>First paragraph&lt;/P::first-line>&lt;/DIV::first-line>&lt;/P>
  &lt;P>&lt;P::first-line>Second paragraph&lt;/P::first-line>&lt;/P>
&lt;/DIV>
</pre>

<p>The <code>::first-line</code> pseudo-element is similar to an
    inline-level element, but with certain restrictions. In CSS, the
    following properties apply to a <code>::first-line</code>
    pseudo-element: font properties, color property, background
    properties, 'word-spacing', 'letter-spacing', 'text-decoration',
    'vertical-align', 'text-transform', 'line-height'. UAs may apply other
    properties as well.</p>


<h4><a name=first-letter>7.2. The ::first-letter pseudo-element</a></h4>

<p>The <code>::first-letter</code> pseudo-element represents the first
    letter of the first line of a block, if it is not preceded by any
    other content (such as images or inline tables) on its line. The
    ::first-letter pseudo-element may be used for "initial caps" and "drop
    caps", which are common typographical effects. This type of initial
    letter is similar to an inline-level element if its 'float' property
    is 'none'; otherwise, it is similar to a floated element.</p>

<p>In CSS, these are the properties that apply to <code>::first-letter</code>
    pseudo-elements: font properties, 'text-decoration', 'text-transform',
    'letter-spacing', 'word-spacing' (when appropriate), 'line-height',
    'float', 'vertical-align' (only if 'float' is 'none'), margin
    properties, padding properties, border properties, color property,
    background properties.  UAs may apply other properties as well.  To
    allow UAs to render a typographically correct drop cap or initial cap,
    the UA may choose a line-height, width and height based on the shape
    of the letter, unlike for normal elements.</p>

<div class="example">
    <p>Example:</p>
    <p>This example shows a possible rendering of an initial cap. Note
        that the 'line-height' that is inherited by the <code>::first-letter</code>
        pseudo-element is 1.1, but the UA in this example has computed the
        height of the first letter differently, so that it doesn't cause any
        unnecessary space between the first two lines. Also note that the
        fictional start tag of the first letter is inside the <span>span</span>, and thus
        the font weight of the first letter is normal, not bold as the <span>span</span>:
    <pre>
p { line-height: 1.1 }
p::first-letter { font-size: 3em; font-weight: normal }
span { font-weight: bold }
...
&lt;p>&lt;span>Het hemelsche&lt;/span> gerecht heeft zich ten lange lesten&lt;br>
Erbarremt over my en mijn benaeuwde vesten&lt;br>
En arme burgery, en op mijn volcx gebed&lt;br>
En dagelix geschrey de bange stad ontzet.
</pre>
    <div class="figure">
        <p><img src="initial-cap.png" alt="Image illustrating the ::first-letter pseudo-element">
    </div>
</div>

<div class="example">
    <p>The following CSS will make a drop cap initial letter span about two lines:</p>

    <pre>
&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"&gt;
&lt;HTML&gt;
 &lt;HEAD&gt;
  &lt;TITLE&gt;Drop cap initial letter&lt;/TITLE&gt;
  &lt;STYLE type="text/css"&gt;
   P               { font-size: 12pt; line-height: 1.2 }
   P::first-letter { font-size: 200%; font-weight: bold; float: left }
   SPAN            { text-transform: uppercase }
  &lt;/STYLE&gt;
 &lt;/HEAD&gt;
 &lt;BODY&gt;
  &lt;P&gt;&lt;SPAN&gt;The first&lt;/SPAN&gt; few words of an article
    in The Economist.&lt;/P&gt;
 &lt;/BODY&gt;
&lt;/HTML&gt;
</pre>

    <p>This example might be formatted as follows:</p>

    <div class="figure">
        <P><img src="first-letter.gif" alt="Image illustrating the combined effect of the ::first-letter and ::first-line pseudo-elements"></p>
    </div>

    <p>The <span class="index-inst" title="fictional tag
sequence">fictional tag sequence</span> is:</p>

    <pre>
&lt;P&gt;
&lt;SPAN&gt;
&lt;P::first-letter&gt;
T
&lt;/P::first-letter&gt;he first
&lt;/SPAN&gt;
few words of an article in the Economist.
&lt;/P&gt;
</pre>

    <p>Note that the <code>::first-letter</code> pseudo-element tags abut
        the content (i.e., the initial character), while the ::first-line
        pseudo-element start tag is inserted right after the start tag of the
        block element.</p> </div>

<p>In order to achieve traditional drop caps formatting, user agents
    may approximate font sizes, for example to align baselines. Also, the
    glyph outline may be taken into account when formatting.</p>

<p>Punctuation (i.e, characters defined in Unicode in the "open" (Ps),
    "close" (Pe), "initial" (Pi). "final" (Pf) and "other" (Po)
    punctuation classes), that precedes or follows the first letter should
    be included. <a href="#refsUNICODE">[UNICODE]</a></p>

<div class="figure">
    <P><img src="first-letter2.gif" alt="Quotes that precede the
first letter should be included."></p>
</div>

<p>The <code>::first-letter</code> also applies if the first letter is
    in fact a digit, e.g., the "6" in "67 million dollars is a lot of
    money."</p>

<p>In CSS, the <code>::first-letter</code> pseudo-element applies to
    block, list-item, table-cell, table-caption, and inline-block
    elements. <span class="note">A future version of this specification
may allow this pesudo-element to apply to more element
types.</span></p>

<p>The <code>::first-letter</code> pseudo-element can be used with all
    such elements that contain text, or that have a descendant in the same
    flow that contains text. A UA should act as if the fictional start tag
    of the ::first-letter pseudo-element is just before the first text of
    the element, even if that first text is in a descendant.</p>

<div class="example">
    <p>Example:</p>
    <p>The fictional tag sequence for this HTMLfragment:
    <pre>&lt;div>
&lt;p>The first text.</pre>
    <p>is:
    <pre>&lt;div>
&lt;p>&lt;div::first-letter>&lt;p::first-letter>T&lt;/...>&lt;/...>he first text.</pre>
</div>

<p>The first letter of a table-cell or inline-block cannot be the
    first letter of an ancestor element. Thus, in <code>&lt;DIV&gt;&lt;P
        STYLE="display: inline-block">Hello&lt;BR&gt;Goodbye&lt;/P&gt;
        etcetera&lt;/DIV&gt;</code> the first letter of the <code>div</code> is not the
    letter "H". In fact, the <code>div</code> doesn't have a first letter.

<p>The first letter must occur on the <a
    href="#first-formatted-line">first formatted line.</a> For example, in
    this fragment: <code>&lt;p&gt&lt;br&gt;First...</code> the first line
    doesn't contain any letters and <code>::first-letter</code> doesn't
    match anything (assuming the default style for <code>br</code> in HTML
    4). In particular, it does not match the "F" of "First."

<p>In CSS, if an element is a list item ('display: list-item'), the
    <code>::first-letter</code> applies to the first letter in the
    principal box after the marker. UAs may ignore
    <code>::first-letter</code> on list items with 'list-style-position:
    inside'. If an element has <code>::before</code> or
    <code>::after</code> content, the <code>::first-letter</code> applies
    to the first letter of the element <em>including</em> that content.

<div class="example">
    <p>Example:</p>
    <p>After the rule 'p::before {content: "Note: "}', the selector
        'p::first-letter' matches the "N" of "Note".</p>
</div>

<p>Some languages may have specific rules about how to treat certain
    letter combinations. In Dutch, for example, if the letter combination
    "ij" appears at the beginning of a word, both letters should be
    considered within the <code>::first-letter</code> pseudo-element.

<p>If the letters that would form the ::first-letter are not in the
    same element, such as "'T" in <code>&lt;p>'&lt;em>T...</code>, the UA
    may create a ::first-letter pseudo-element from one of the elements,
    both elements, or simply not create a pseudo-element.</p>

<p>Similarly, if the first letter(s) of the block are not at the start
    of the line (for example due to bidirectional reordering), then the UA
    need not create the pseudo-element(s).

<div class="example">
    <p>Example:</p>
    <p><a name="overlapping-example">The following example</a> illustrates
        how overlapping pseudo-elements may interact.  The first letter of
        each P element will be green with a font size of '24pt'. The rest of
        the first formatted line will be 'blue' while the rest of the
        paragraph will be 'red'.</p>

    <pre>p { color: red; font-size: 12pt }
p::first-letter { color: green; font-size: 200% }
p::first-line { color: blue }

&lt;P&gt;Some text that ends up on two lines&lt;/P&gt;</pre>

    <p>Assuming that a line break will occur before the word "ends", the
        <span class="index-inst" title="fictional tag sequence">fictional tag
sequence</span> for this fragment might be:</p>

    <pre>&lt;P&gt;
&lt;P::first-line&gt;
&lt;P::first-letter&gt;
S
&lt;/P::first-letter&gt;ome text that
&lt;/P::first-line&gt;
ends up on two lines
&lt;/P&gt;</pre>

    <p>Note that the <code>::first-letter</code> element is inside the <code>::first-line</code>
        element.  Properties set on <code>::first-line</code> are inherited by
        <code>::first-letter</code>, but are overridden if the same property is set on
        <code>::first-letter</code>.</p>
</div>


<h4><a name=UIfragments>7.3.</a> <a name=selection>The ::selection pseudo-element</a></h4>

<p>The <code>::selection</code> pseudo-element applies to the portion
    of a document that has been highlighted by the user. This also
    applies, for example, to selected text within an editable text
    field. This pseudo-element should not be confused with the <code><a
        href="#checked">:checked</a></code> pseudo-class (which used to be
    named <code>:selected</code>)

<p>Although the <code>::selection</code> pseudo-element is dynamic in
    nature, and is altered by user action, it is reasonable to expect that
    when a UA re-renders to a static medium (such as a printed page, see
    <a href="#refsCSS21">[CSS21]</a>) which was originally rendered to a
    dynamic medium (like screen), the UA may wish to transfer the current
    <code>::selection</code> state to that other medium, and have all the
    appropriate formatting and rendering take effect as well. This is not
    required &mdash; UAs may omit the <code>::selection</code>
    pseudo-element for static media.

<p>These are the CSS properties that apply to <code>::selection</code>
    pseudo-elements: color, background, cursor (optional), outline
    (optional). The computed value of the 'background-image' property on
    <code>::selection</code> may be ignored.


<h4><a name=gen-content>7.4. The ::before and ::after pseudo-elements</a></h4>

<p>The <code>::before</code> and <code>::after</code> pseudo-elements
    can be used to describe generated content before or after an element's
    content. They are explained in CSS 2.1 <a
        href="#refsCSS21">[CSS21]</a>.</p>

<p>When the <code>::first-letter</code> and <code>::first-line</code>
    pseudo-elements are combined with <code>::before</code> and
    <code>::after</code>, they apply to the first letter or line of the
    element including the inserted text.</p>

<h2><a name=combinators>8. Combinators</a></h2>

<h3><a name=descendant-combinators>8.1. Descendant combinator</a></h3>

<p>At times, authors may want selectors to describe an element that is
    the descendant of another element in the document tree (e.g., "an
    <code>EM</code> element that is contained within an <code>H1</code>
    element"). Descendant combinators express such a relationship. A
    descendant combinator is <a href="#whitespace">white space</a> that
    separates two sequences of simple selectors.  A selector of the form
    "<code>A B</code>" represents an element <code>B</code> that is an
    arbitrary descendant of some ancestor element <code>A</code>.

<div class="example">
    <p>Examples:</p>
    <p>For example, consider the following selector:</p>
    <pre>h1 em</pre>
    <p>It represents an <code>em</code> element being the descendant of
        an <code>h1</code> element. It is a correct and valid, but partial,
        description of the following fragment:</p>
    <pre>&lt;h1&gt;This &lt;span class="myclass"&gt;headline
is &lt;em&gt;very&lt;/em&gt; important&lt;/span&gt;&lt;/h1&gt;</pre>
    <p>The following selector:</p>
    <pre>div * p</pre>
    <p>represents a <code>p</code> element that is a grandchild or later
        descendant of a <code>div</code> element. Note the whitespace on
        either side of the "*" is not part of the universal selector; the
        whitespace is a combinator indicating that the DIV must be the
        ancestor of some element, and that that element must be an ancestor
        of the P.</p>
    <p>The following selector, which combines descendant combinators and
        <a href="#attribute-selectors">attribute selectors</a>, represents an
        element that (1) has the <code>href</code> attribute set and (2) is
        inside a <code>p</code> that is itself inside a <code>div</code>:</p>
    <pre>div p *[href]</pre>
</div>

<h3><a name=child-combinators>8.2. Child combinators</a></h3>

<p>A <dfn>child combinator</dfn> describes a childhood relationship
    between two elements. A child combinator is made of the
    &quot;greater-than sign&quot; (<code>&gt;</code>) character and
    separates two sequences of simple selectors.


<div class="example">
    <p>Examples:</p>
    <p>The following selector represents a <code>p</code> element that is
        child of <code>body</code>:</p>
    <pre>body &gt; p</pre>
    <p>The following example combines descendant combinators and child
        combinators.</p>
    <pre>div ol&gt;li p</pre><!-- LEAVE THOSE SPACES OUT! see below -->
    <p>It represents a <code>p</code> element that is a descendant of an
        <code>li</code> element; the <code>li</code> element must be the
        child of an <code>ol</code> element; the <code>ol</code> element must
        be a descendant of a <code>div</code>. Notice that the optional white
        space around the "&gt;" combinator has been left out.</p>
</div>

<p>For information on selecting the first child of an element, please
    see the section on the <code><a
        href="#structural-pseudos">:first-child</a></code> pseudo-class
    above.</p>

<h3><a name=sibling-combinators>8.3. Sibling combinators</a></h3>

<p>There are two different sibling combinators: the adjacent sibling
    combinator and the general sibling combinator. In both cases,
    non-element nodes (e.g. text between elements) are ignored when
    considering adjacency of elements.</p>

<h4><a name=adjacent-sibling-combinators>8.3.1. Adjacent sibling combinator</a></h4>

<p>The adjacent sibling combinator is made of the &quot;plus
    sign&quot; (U+002B, <code>+</code>) character that separates two
    sequences of simple selectors. The elements represented by the two
    sequences share the same parent in the document tree and the element
    represented by the first sequence immediately precedes the element
    represented by the second one.</p>

<div class="example">
    <p>Examples:</p>
    <p>The following selector represents a <code>p</code> element
        immediately following a <code>math</code> element:</p>
    <pre>math + p</pre>
    <p>The following selector is conceptually similar to the one in the
        previous example, except that it adds an attribute selector &mdash; it
        adds a constraint to the <code>h1</code> element, that it must have
        <code>class="opener"</code>:</p>
    <pre>h1.opener + h2</pre>
</div>


<h4><a name=general-sibling-combinators>8.3.2. General sibling combinator</a></h4>

<p>The general sibling combinator is made of the &quot;tilde&quot;
    (U+007E, <code>~</code>) character that separates two sequences of
    simple selectors. The elements represented by the two sequences share
    the same parent in the document tree and the element represented by
    the first sequence precedes (not necessarily immediately) the element
    represented by the second one.</p>

<div class="example">
    <p>Example:</p>
    <pre>h1 ~ pre</pre>
    <p>represents a <code>pre</code> element following an <code>h1</code>. It
        is a correct and valid, but partial, description of:</p>
    <pre>&lt;h1&gt;Definition of the function a&lt;/h1&gt;
&lt;p&gt;Function a(x) has to be applied to all figures in the table.&lt;/p&gt;
&lt;pre&gt;function a(x) = 12x/13.5&lt;/pre&gt;</pre>
</div>

<h2><a name=specificity>9. Calculating a selector's specificity</a></h2>

<p>A selector's specificity is calculated as follows:</p>

<ul>
    <li>count the number of ID selectors in the selector (= a)</li>
    <li>count the number of class selectors, attributes selectors, and pseudo-classes in the selector (= b)</li>
    <li>count the number of element names in the selector (= c)</li>
    <li>ignore pseudo-elements</li>
</ul>

<p>Selectors inside <a href="#negation">the negation pseudo-class</a>
    are counted like any other, but the negation itself does not count as
    a pseudo-class.</p>

<p>Concatenating the three numbers a-b-c (in a number system with a
    large base) gives the specificity.</p>

<div class="example">
    <p>Examples:</p>
    <pre>*               /* a=0 b=0 c=0 -&gt; specificity =   0 */
LI              /* a=0 b=0 c=1 -&gt; specificity =   1 */
UL LI           /* a=0 b=0 c=2 -&gt; specificity =   2 */
UL OL+LI        /* a=0 b=0 c=3 -&gt; specificity =   3 */
H1 + *[REL=up]  /* a=0 b=1 c=1 -&gt; specificity =  11 */
UL OL LI.red    /* a=0 b=1 c=3 -&gt; specificity =  13 */
LI.red.level    /* a=0 b=2 c=1 -&gt; specificity =  21 */
#x34y           /* a=1 b=0 c=0 -&gt; specificity = 100 */
#s12:not(FOO)   /* a=1 b=0 c=1 -&gt; specificity = 101 */
</pre>
</div>

<p class="note"><strong>Note:</strong> the specificity of the styles
    specified in an HTML <code>style</code> attribute is described in CSS
    2.1. <a href="#refsCSS21">[CSS21]</a>.</p>

<h2><a name=w3cselgrammar>10. The grammar of Selectors</a></h2>

<h3><a name=grammar>10.1. Grammar</a></h3>

<p>The grammar below defines the syntax of Selectors.  It is globally
    LL(1) and can be locally LL(2) (but note that most UA's should not use
    it directly, since it doesn't express the parsing conventions). The
    format of the productions is optimized for human consumption and some
    shorthand notations beyond Yacc (see <a href="#refsYACC">[YACC]</a>)
    are used:</p>

<ul>
    <li><b>*</b>: 0 or more
    <li><b>+</b>: 1 or more
    <li><b>?</b>: 0 or 1
    <li><b>|</b>: separates alternatives
    <li><b>[ ]</b>: grouping </li>
</ul>

<p>The productions are:</p>

<pre>selectors_group
  : selector [ COMMA S* selector ]*
  ;

selector
  : simple_selector_sequence [ combinator simple_selector_sequence ]*
  ;

combinator
  /* combinators can be surrounded by white space */
  : PLUS S* | GREATER S* | TILDE S* | S+
  ;

simple_selector_sequence
  : [ type_selector | universal ]
    [ HASH | class | attrib | pseudo | negation ]*
  | [ HASH | class | attrib | pseudo | negation ]+
  ;

type_selector
  : [ namespace_prefix ]? element_name
  ;

namespace_prefix
  : [ IDENT | '*' ]? '|'
  ;

element_name
  : IDENT
  ;

universal
  : [ namespace_prefix ]? '*'
  ;

class
  : '.' IDENT
  ;

attrib
  : '[' S* [ namespace_prefix ]? IDENT S*
        [ [ PREFIXMATCH |
            SUFFIXMATCH |
            SUBSTRINGMATCH |
            '=' |
            INCLUDES |
            DASHMATCH ] S* [ IDENT | STRING ] S*
        ]? ']'
  ;

pseudo
  /* '::' starts a pseudo-element, ':' a pseudo-class */
  /* Exceptions: :first-line, :first-letter, :before and :after. */
  /* Note that pseudo-elements are restricted to one per selector and */
  /* occur only in the last simple_selector_sequence. */
  : ':' ':'? [ IDENT | functional_pseudo ]
  ;

functional_pseudo
  : FUNCTION S* expression ')'
  ;

expression
  /* In CSS3, the expressions are identifiers, strings, */
  /* or of the form "an+b" */
  : [ [ PLUS | '-' | DIMENSION | NUMBER | STRING | IDENT ] S* ]+
  ;

negation
  : NOT S* negation_arg S* ')'
  ;

negation_arg
  : type_selector | universal | HASH | class | attrib | pseudo
  ;</pre>


<h3><a name=lex>10.2. Lexical scanner</a></h3>

<p>The following is the <a name=x3>tokenizer</a>, written in Flex (see
    <a href="#refsFLEX">[FLEX]</a>) notation. The tokenizer is
    case-insensitive.</p>

<p>The two occurrences of "\377" represent the highest character
    number that current versions of Flex can deal with (decimal 255). They
    should be read as "\4177777" (decimal 1114111), which is the highest
    possible code point in Unicode/ISO-10646. <a
        href="#refsUNICODE">[UNICODE]</a></p>

<pre>%option case-insensitive

ident     [-]?{nmstart}{nmchar}*
name      {nmchar}+
nmstart   [_a-z]|{nonascii}|{escape}
nonascii  [^\0-\177]
unicode   \\[0-9a-f]{1,6}(\r\n|[ \n\r\t\f])?
escape    {unicode}|\\[^\n\r\f0-9a-f]
nmchar    [_a-z0-9-]|{nonascii}|{escape}
num       [0-9]+|[0-9]*\.[0-9]+
string    {string1}|{string2}
string1   \"([^\n\r\f\\"]|\\{nl}|{nonascii}|{escape})*\"
string2   \'([^\n\r\f\\']|\\{nl}|{nonascii}|{escape})*\'
invalid   {invalid1}|{invalid2}
invalid1  \"([^\n\r\f\\"]|\\{nl}|{nonascii}|{escape})*
invalid2  \'([^\n\r\f\\']|\\{nl}|{nonascii}|{escape})*
nl        \n|\r\n|\r|\f
w         [ \t\r\n\f]*

%%

[ \t\r\n\f]+     return S;

"~="             return INCLUDES;
"|="             return DASHMATCH;
"^="             return PREFIXMATCH;
"$="             return SUFFIXMATCH;
"*="             return SUBSTRINGMATCH;
{ident}          return IDENT;
{string}         return STRING;
{ident}"("       return FUNCTION;
{num}            return NUMBER;
"#"{name}        return HASH;
{w}"+"           return PLUS;
{w}"&gt;"           return GREATER;
{w}","           return COMMA;
{w}"~"           return TILDE;
":not("          return NOT;
@{ident}         return ATKEYWORD;
{invalid}        return INVALID;
{num}%           return PERCENTAGE;
{num}{ident}     return DIMENSION;
"&lt;!--"           return CDO;
"--&gt;"            return CDC;

"url("{w}{string}{w}")"                           return URI;
"url("{w}([!#$%&*-~]|{nonascii}|{escape})*{w}")"  return URI;
U\+[0-9a-f?]{1,6}(-[0-9a-f]{1,6})?                return UNICODE_RANGE;

\/\*[^*]*\*+([^/*][^*]*\*+)*\/                    /* ignore comments */

.                return *yytext;</pre>



<h2><a name=downlevel>11. Namespaces and down-level clients</a></h2>

<p>An important issue is the interaction of CSS selectors with XML
    documents in web clients that were produced prior to this
    document. Unfortunately, due to the fact that namespaces must be
    matched based on the URI which identifies the namespace, not the
    namespace prefix, some mechanism is required to identify namespaces in
    CSS by their URI as well. Without such a mechanism, it is impossible
    to construct a CSS style sheet which will properly match selectors in
    all cases against a random set of XML documents. However, given
    complete knowledge of the XML document to which a style sheet is to be
    applied, and a limited use of namespaces within the XML document, it
    is possible to construct a style sheet in which selectors would match
    elements and attributes correctly.</p>

<p>It should be noted that a down-level CSS client will (if it
    properly conforms to CSS forward compatible parsing rules) ignore all
    <code>@namespace</code> at-rules, as well as all style rules that make
    use of namespace qualified element type or attribute selectors. The
    syntax of delimiting namespace prefixes in CSS was deliberately chosen
    so that down-level CSS clients would ignore the style rules rather
    than possibly match them incorrectly.</p>

<p>The use of default namespaces in CSS makes it possible to write
    element type selectors that will function in both namespace aware CSS
    clients as well as down-level clients. It should be noted that
    down-level clients may incorrectly match selectors against XML
    elements in other namespaces.</p>

<p>The following are scenarios and examples in which it is possible to
    construct style sheets which would function properly in web clients
    that do not implement this proposal.</p>

<ol>
    <li>

        <p>The XML document does not use namespaces.</p>

        <ul>

            <li>In this case, it is obviously not necessary to declare or use
                namespaces in the style sheet. Standard CSS element type and
                attribute selectors will function adequately in a down-level
                client.</li>

            <li>In a CSS namespace aware client, the default behavior of
                element selectors matching without regard to namespace will
                function properly against all elements, since no namespaces are
                present. However, the use of specific element type selectors that
                match only elements that have no namespace ("<code>|name</code>")
                will guarantee that selectors will match only XML elements that do
                not have a declared namespace. </li>

        </ul>

    </li>

    <li>

        <p>The XML document defines a single, default namespace used
            throughout the document. No namespace prefixes are used in element
            names.</p>

        <ul>

            <li>In this case, a down-level client will function as if
                namespaces were not used in the XML document at all. Standard CSS
                element type and attribute selectors will match against all
                elements. </li>

        </ul>

    </li>

    <li>

        <p>The XML document does <b>not</b> use a default namespace, all
            namespace prefixes used are known to the style sheet author, and
            there is a direct mapping between namespace prefixes and namespace
            URIs. (A given prefix may only be mapped to one namespace URI
            throughout the XML document; there may be multiple prefixes mapped
            to the same URI).</p>

        <ul>

            <li>In this case, the down-level client will view and match
                element type and attribute selectors based on their fully
                qualified name, not the local part as outlined in the <a
                    href="#typenmsp">Type selectors and Namespaces</a> section. CSS
                selectors may be declared using an escaped colon "<code>\:</code>"
                to describe the fully qualified names, e.g.
                "<code>html\:h1</code>" will match
                <code>&lt;html:h1&gt;</code>. Selectors using the qualified name
                will only match XML elements that use the same prefix. Other
                namespace prefixes used in the XML that are mapped to the same URI
                will not match as expected unless additional CSS style rules are
                declared for them.</li>

            <li>Note that selectors declared in this fashion will
                <em>only</em> match in down-level clients. A CSS namespace aware
                client will match element type and attribute selectors based on
                the name's local part. Selectors declared with the fully
                qualified name will not match (unless there is no namespace prefix
                in the fully qualified name).</li>

        </ul>

    </li>

</ol>

<p>In other scenarios: when the namespace prefixes used in the XML are
    not known in advance by the style sheet author; or a combination of
    elements with no namespace are used in conjunction with elements using
    a default namespace; or the same namespace prefix is mapped to
    <em>different</em> namespace URIs within the same document, or in
    different documents; it is impossible to construct a CSS style sheet
    that will function properly against all elements in those documents,
    unless, the style sheet is written using a namespace URI syntax (as
    outlined in this document or similar) and the document is processed by
    a CSS and XML namespace aware client.</p>

<h2><a name=profiling>12. Profiles</a></h2>

<p>Each specification using Selectors must define the subset of W3C
    Selectors it allows and excludes, and describe the local meaning of
    all the components of that subset.</p>

<p>Non normative examples:

<div class="profile">
    <table class="tprofile">
        <tbody>
        <tr>
            <th class="title" colspan=2>Selectors profile</th></tr>
        <tr>
            <th>Specification</th>
            <td>CSS level 1</td></tr>
        <tr>
            <th>Accepts</th>
            <td>type selectors<br>class selectors<br>ID selectors<br>:link,
                :visited and :active pseudo-classes<br>descendant combinator
                <br>::first-line and ::first-letter pseudo-elements</td></tr>
        <tr>
            <th>Excludes</th>
            <td>

                <p>universal selector<br>attribute selectors<br>:hover and :focus
                    pseudo-classes<br>:target pseudo-class<br>:lang() pseudo-class<br>all UI
                    element states pseudo-classes<br>all structural
                    pseudo-classes<br>negation pseudo-class<br>all
                    UI element fragments pseudo-elements<br>::before and ::after
                    pseudo-elements<br>child combinators<br>sibling combinators

                <p>namespaces</td></tr>
        <tr>
            <th>Extra constraints</th>
            <td>only one class selector allowed per sequence of simple
                selectors</td></tr></tbody></table><br><br>
    <table class="tprofile">
        <tbody>
        <tr>
            <th class="title" colspan=2>Selectors profile</th></tr>
        <tr>
            <th>Specification</th>
            <td>CSS level 2</td></tr>
        <tr>
            <th>Accepts</th>
            <td>type selectors<br>universal selector<br>attribute presence and
                values selectors<br>class selectors<br>ID selectors<br>:link, :visited,
                :active, :hover, :focus, :lang() and :first-child pseudo-classes
                <br>descendant combinator<br>child combinator<br>adjacent sibling
                combinator<br>::first-line and ::first-letter pseudo-elements<br>::before
                and ::after pseudo-elements</td></tr>
        <tr>
            <th>Excludes</th>
            <td>

                <p>content selectors<br>substring matching attribute
                    selectors<br>:target pseudo-classes<br>all UI element
                    states pseudo-classes<br>all structural pseudo-classes other
                    than :first-child<br>negation pseudo-class<br>all UI element
                    fragments pseudo-elements<br>general sibling combinators

                <p>namespaces</td></tr>
        <tr>
            <th>Extra constraints</th>
            <td>more than one class selector per sequence of simple selectors (CSS1
                constraint) allowed</td></tr></tbody></table>

    <p>In CSS, selectors express pattern matching rules that determine which style
        rules apply to elements in the document tree.

    <p>The following selector (CSS level 2) will <b>match</b> all anchors <code>a</code>
        with attribute <code>name</code> set inside a section 1 header <code>h1</code>:
    <pre>h1 a[name]</pre>

    <p>All CSS declarations attached to such a selector are applied to elements
        matching it. </div>

<div class="profile">
    <table class="tprofile">
        <tbody>
        <tr>
            <th class="title" colspan=2>Selectors profile</th></tr>
        <tr>
            <th>Specification</th>
            <td>STTS 3</td>
        </tr>
        <tr>
            <th>Accepts</th>
            <td>

                <p>type selectors<br>universal selectors<br>attribute selectors<br>class
                    selectors<br>ID selectors<br>all structural pseudo-classes<br>
                    all combinators

                <p>namespaces</td></tr>
        <tr>
            <th>Excludes</th>
            <td>non-accepted pseudo-classes<br>pseudo-elements<br></td></tr>
        <tr>
            <th>Extra constraints</th>
            <td>some selectors and combinators are not allowed in fragment
                descriptions on the right side of STTS declarations.</td></tr></tbody></table>

    <p>Selectors can be used in STTS 3 in two different
        manners:
    <ol>
        <li>a selection mechanism equivalent to CSS selection mechanism: declarations
            attached to a given selector are applied to elements matching that selector,
        <li>fragment descriptions that appear on the right side of declarations.
        </li></ol></div>

<h2><a name=Conformance></a>13. Conformance and requirements</h2>

<p>This section defines conformance with the present specification only.

<p>The inability of a user agent to implement part of this specification due to
    the limitations of a particular device (e.g., non interactive user agents will
    probably not implement dynamic pseudo-classes because they make no sense without
    interactivity) does not imply non-conformance.

<p>All specifications reusing Selectors must contain a <a
    href="#profiling">Profile</a> listing the
    subset of Selectors it accepts or excludes, and describing the constraints
    it adds to the current specification.

<p>Invalidity is caused by a parsing error, e.g. an unrecognized token or a token
    which is not allowed at the current parsing point.

<p>User agents must observe the rules for handling parsing errors:
<ul>
    <li>a simple selector containing an undeclared namespace prefix is invalid</li>
    <li>a selector containing an invalid simple selector, an invalid combinator
        or an invalid token is invalid. </li>
    <li>a group of selectors containing an invalid selector is invalid.</li>
</ul>

<p>Specifications reusing Selectors must define how to handle parsing
    errors. (In the case of CSS, the entire rule in which the selector is
    used is dropped.)</p>

<!-- Apparently all these references are out of date:
<p>Implementations of this specification must behave as
"recipients of text data" as defined by <a href="#refsCWWW">[CWWW]</a>
when parsing selectors and attempting matches. (In particular,
implementations must assume the data is normalized and must not
normalize it.) Normative rules for matching strings are defined in
<a href="#refsCWWW">[CWWW]</a> and <a
href="#refsUNICODE">[UNICODE]</a> and apply to implementations of this
specification.</p>-->

<h2><a name=Tests></a>14. Tests</h2>

<p>This specification has <a
    href="http://www.w3.org/Style/CSS/Test/CSS3/Selectors/current/">a test
    suite</a> allowing user agents to verify their basic conformance to
    the specification. This test suite does not pretend to be exhaustive
    and does not cover all possible combined cases of Selectors.</p>

<h2><a name=ACKS></a>15. Acknowledgements</h2>

<p>The CSS working group would like to thank everyone who has sent
    comments on this specification over the years.</p>

<p>The working group would like to extend special thanks to Donna
    McManus, Justin Baker, Joel Sklar, and Molly Ives Brower who perfermed
    the final editorial review.</p>

<h2><a name=references>16. References</a></h2>

<dl class="refs">

    <dt>[CSS1]
    <dd><a name=refsCSS1></a> Bert Bos, H&aring;kon Wium Lie; "<cite>Cascading Style Sheets, level 1</cite>", W3C Recommendation, 17 Dec 1996, revised 11 Jan 1999
    <dd>(<code><a href="http://www.w3.org/TR/REC-CSS1">http://www.w3.org/TR/REC-CSS1</a></code>)

    <dt>[CSS21]
    <dd><a name=refsCSS21></a> Bert Bos, Tantek &Ccedil;elik, Ian Hickson, H&aring;kon Wium Lie, editors; "<cite>Cascading Style Sheets, level 2 revision 1</cite>", W3C Working Draft, 13 June 2005
    <dd>(<code><a href="http://www.w3.org/TR/CSS21">http://www.w3.org/TR/CSS21</a></code>)

    <dt>[CWWW]
    <dd><a name=refsCWWW></a> Martin J. D&uuml;rst, Fran&ccedil;ois Yergeau, Misha Wolf, Asmus Freytag, Tex Texin, editors; "<cite>Character Model for the World Wide Web</cite>", W3C Recommendation, 15 February 2005
    <dd>(<code><a href="http://www.w3.org/TR/charmod/">http://www.w3.org/TR/charmod/</a></code>)

    <dt>[FLEX]
    <dd><a name="refsFLEX"></a> "<cite>Flex: The Lexical Scanner Generator</cite>", Version 2.3.7, ISBN 1882114213

    <dt>[HTML4]
    <dd><a name="refsHTML4"></a> Dave Ragget, Arnaud Le Hors, Ian Jacobs, editors; "<cite>HTML 4.01 Specification</cite>", W3C Recommendation, 24 December 1999
    <dd>(<a href="http://www.w3.org/TR/html4/"><code>http://www.w3.org/TR/html4/</code></a>)

    <dt>[MATH]
    <dd><a name="refsMATH"></a> Patrick Ion, Robert Miner, editors; "<cite>Mathematical Markup Language (MathML) 1.01</cite>", W3C Recommendation, revision of 7 July 1999
    <dd>(<code><a href="http://www.w3.org/TR/REC-MathML/">http://www.w3.org/TR/REC-MathML/</a></code>)

    <dt>[RFC3066]
    <dd><a name="refsRFC3066"></a> H. Alvestrand; "<cite>Tags for the Identification of Languages</cite>", Request for Comments 3066, January 2001
    <dd>(<a href="http://www.ietf.org/rfc/rfc3066.txt"><code>http://www.ietf.org/rfc/rfc3066.txt</code></a>)

    <dt>[STTS]
    <dd><a name=refsSTTS></a> Daniel Glazman; "<cite>Simple Tree Transformation Sheets 3</cite>", Electricit&eacute; de France, submission to the W3C, 11 November 1998
    <dd>(<code><a href="http://www.w3.org/TR/NOTE-STTS3">http://www.w3.org/TR/NOTE-STTS3</a></code>)

    <dt>[SVG]
    <dd><a name="refsSVG"></a> Jon Ferraiolo, &#34276;&#27810; &#28147;, Dean Jackson, editors; "<cite>Scalable Vector Graphics (SVG) 1.1 Specification</cite>", W3C Recommendation, 14 January 2003
    <dd>(<code><a href="http://www.w3.org/TR/SVG/">http://www.w3.org/TR/SVG/</a></code>)

    <dt>[UNICODE]</dt>
    <dd><a name="refsUNICODE"></a> <cite><a
        href="http://www.unicode.org/versions/Unicode4.1.0/">The Unicode Standard, Version 4.1</a></cite>, The Unicode Consortium. Boston, MA, Addison-Wesley, March 2005. ISBN 0-321-18578-1, as amended by <a href="http://www.unicode.org/versions/Unicode4.0.1/">Unicode 4.0.1</a> and <a href="http://www.unicode.org/versions/Unicode4.1.0/">Unicode  4.1.0</a>.
    <dd>(<code><a href="http://www.unicode.org/versions/">http://www.unicode.org/versions/</a></code>)</dd>

    <dt>[XML10]
    <dd><a name="refsXML10"></a> Tim Bray, Jean Paoli, C. M. Sperberg-McQueen, Eve Maler, Fran&ccedil;ois Yergeau, editors; "<cite>Extensible Markup Language (XML) 1.0 (Third Edition)</cite>", W3C Recommendation, 4 February 2004
    <dd>(<a href="http://www.w3.org/TR/REC-xml/"><code>http://www.w3.org/TR/REC-xml/</code></a>)

    <dt>[XMLNAMES]
    <dd><a name="refsXMLNAMES"></a> Tim Bray, Dave Hollander, Andrew Layman, editors; "<cite>Namespaces in XML</cite>", W3C Recommendation, 14 January 1999
    <dd>(<a href="http://www.w3.org/TR/REC-xml-names/"><code>http://www.w3.org/TR/REC-xml-names/</code></a>)

    <dt>[YACC]
    <dd><a name="refsYACC"></a> S. C. Johnson; "<cite>YACC &mdash; Yet another compiler compiler</cite>", Technical Report, Murray Hill, 1975

</dl>